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Quantum simulation of oscillating neutrinos | Two and three flavor oscillating neutrinos are shown to exhibit the
properties bipartite and tripartite quantum entanglement. The two and three
flavor neutrinos are mapped to qubit states used in quantum information theory.
Such quantum bits of the neutrino state can be encoded on a IBMQ computer using
quantum computing as a tool. We show the implementation of entanglement in the
two neutrino system on the IBM quantum processor. | [
"Abhishek Kumar Jha",
"Akshay Chatla",
"Bindu A. Bambah"
] | [
"IBM"
] | "2020-10-13T15:12:31Z" | 2010.06458v2 |
Phase Analysis on the Error Scaling of Entangled Qubits in a 53-Qubit
System | We have studied carefully the behaviors of entangled qubits on the IBM
Rochester with various connectivities and under a "noisy" environment. A phase
trajectory analysis based on our measurements of the GHZ-like states is
performed. Our results point to an important fact that entangled qubits are
"protected" against environmental noise by a scaling property that impacts only
the weighting of their amplitudes. The reproducibility of most measurements has
been confirmed within a reasonably short gate operation time. But there still
are a few combinations of qubits that show significant entanglement evolution
in the form of transitions between quantum states. The phase trajectory of an
entangled evolution, and the impact of the sudden death of GHZ-like states and
the revival of newly excited states are analyzed in details. All observed
trajectories of entangled qubits arise under the influences of the newly
excited states in a "noisy" intermediate-scale quantum (NISQ) computer. | [
"Wei-Jia Huang",
"Wei-Chen Chien",
"Chien-Hung Cho",
"Che-Chun Huang",
"Tsung-Wei Huang",
"Seng Ghee Tan",
"Chenfeng Cao",
"Bei Zeng",
"Ching-Ray Chang"
] | [
"IBM"
] | "2020-10-13T12:53:15Z" | 2010.06339v2 |
Entanglement and non-locality of four-qubit connected hypergraph states | We study entanglement and non-locality of connected four-qubit hypergraph
states. One obtains the SLOCC classification from the known LU-orbits. We then
consider Mermin's polynomials and show that all four-qubit hypergraph states
exhibit non-local behavior. Finally, we implement some of the corresponding
inequalities on the IBM Quantum Experience. | [
"Grâce Amouzou",
"Jeoffrey Boffelli",
"Hamza Jaffali",
"Kossi Atchonouglo",
"Frédéric Holweck"
] | [
"IBM"
] | "2020-10-07T06:53:13Z" | 2010.03217v1 |
A Hardware-Aware Heuristic for the Qubit Mapping Problem in the NISQ Era | Due to several physical limitations in the realisation of quantum hardware,
today's quantum computers are qualified as Noisy Intermediate-Scale Quantum
(NISQ) hardware. NISQ hardware is characterized by a small number of qubits (50
to a few hundred) and noisy operations. Moreover, current realisations of
superconducting quantum chips do not have the ideal all-to-all connectivity
between qubits but rather at most a nearest-neighbour connectivity. All these
hardware restrictions add supplementary low-level requirements. They need to be
addressed before submitting the quantum circuit to an actual chip. Satisfying
these requirements is a tedious task for the programmer. Instead, the task of
adapting the quantum circuit to a given hardware is left to the compiler. In
this paper, we propose a Hardware-Aware mapping transition algorithm (HA) that
takes the calibration data into account with the aim to improve the overall
fidelity of the circuit. Evaluation results on IBM quantum hardware show that
our HA approach can outperform the state of the art both in terms of the number
of additional gates and circuit fidelity. | [
"Siyuan Niu",
"Adrien Suau",
"Gabriel Staffelbach",
"Aida Todri-Sanial"
] | [
"IBM"
] | "2020-10-06T07:03:35Z" | 2010.03397v1 |
Application of a Quantum Search Algorithm to High- Energy Physics Data
at the Large Hadron Collider | We demonstrate a novel method for applying a scientific quantum algorithm -
the Grover Algorithm (GA) - to search for rare events in proton-proton
collisions at 13 TeV collision energy using CERN's Large Hadron Collider. The
search is of an unsorted database from the ATLAS detector in the form of ATLAS
Open Data. As indicated by the Higgs boson decay channel $H\rightarrow
ZZ^*\rightarrow 4l$, the detection of four leptons in one event may be used to
reconstruct the Higgs boson and, more importantly, evince Higgs boson decay to
some new phenomena, such as $H\rightarrow ZZ_d \rightarrow 4l$. In searching
the dataset for collisions resulting in the detection of four leptons, the
study demonstrates the effectiveness and potential of applying quantum
computing to high-energy particle physics. Using a Jupyter Notebook, a
classical simulation of GA, and multiple quantum computers, each with several
qubits, it is demonstrated that this application makes the proper selection in
the unsorted dataset. The implementation of the method on several classical
simulators and on several of IBM's quantum computers using the IBM Qiskit Open
Source Software exhibits the promising prospects of quantum computing in
high-energy physics. | [
"Anthony E. Armenakas",
"Oliver K. Baker"
] | [
"IBM"
] | "2020-10-01T19:23:36Z" | 2010.00649v1 |
Demonstrating the power of quantum computers, certification of highly
entangled measurements and scalable quantum nonlocality | Increasingly sophisticated quantum computers motivate the exploration of
their abilities in certifying genuine quantum phenomena. Here, we demonstrate
the power of state-of-the-art IBM quantum computers in correlation experiments
inspired by quantum networks. Our experiments feature up to 12 qubits and
require the implementation of paradigmatic Bell-State Measurements for scalable
entanglement-swapping. First, we demonstrate quantum correlations that defy
classical models in up to nine-qubit systems while only assuming that the
quantum computer operates on qubits. Harvesting these quantum advantages, we
are able to certify 82 basis elements as entangled in a 512-outcome
measurement. Then, we relax the qubit assumption and consider quantum
nonlocality in a scenario with multiple independent entangled states arranged
in a star configuration. We report quantum violations of source-independent
Bell inequalities for up to ten qubits. Our results demonstrate the ability of
quantum computers to outperform classical limitations and certify scalable
entangled measurements. | [
"Elisa Bäumer",
"Nicolas Gisin",
"Armin Tavakoli"
] | [
"IBM"
] | "2020-09-29T13:59:49Z" | 2009.14028v2 |
Quantum computed moments correction to variational estimates | The variational principle of quantum mechanics is the backbone of hybrid
quantum computing for a range of applications. However, as the problem size
grows, quantum logic errors and the effect of barren plateaus overwhelm the
quality of the results. There is now a clear focus on strategies that require
fewer quantum circuit steps and are robust to device errors. Here we present an
approach in which problem complexity is transferred to dynamic quantities
computed on the quantum processor - Hamiltonian moments, $\langle H^n\rangle$.
From these quantum computed moments, estimates of the ground-state energy are
obtained using the "infinum" theorem from Lanczos cumulant expansions which
manifestly correct the associated variational calculation. With system dynamics
encoded in the moments the burden on the trial-state quantum circuit depth is
eased. The method is introduced and demonstrated on 2D quantum magnetism models
on lattices up to 5 $\times$ 5 (25 qubits) implemented on IBM Quantum
superconducting qubit devices. Moments were quantum computed to fourth order
with respect to a parameterised antiferromagnetic trial-state. A comprehensive
comparison with benchmark variational calculations was performed, including
over an ensemble of random coupling instances. The results showed that the
infinum estimate consistently outperformed the benchmark variational approach
for the same trial-state. These initial investigations suggest that the quantum
computed moments approach has a high degree of stability against trial-state
variation, quantum gate errors and shot noise, all of which bodes well for
further investigation and applications of the approach. | [
"Harish J. Vallury",
"Michael A. Jones",
"Charles D. Hill",
"Lloyd C. L. Hollenberg"
] | [
"IBM"
] | "2020-09-28T08:39:05Z" | 2009.13140v3 |
Efficient Quantum State Sample Tomography with Basis-dependent
Neural-networks | We use a meta-learning neural-network approach to analyse data from a
measured quantum state. Once our neural network has been trained it can be used
to efficiently sample measurements of the state in measurement bases not
contained in the training data. These samples can be used calculate expectation
values and other useful quantities. We refer to this process as "state sample
tomography". We encode the state's measurement outcome distributions using an
efficiently parameterized generative neural network. This allows each stage in
the tomography process to be performed efficiently even for large systems. Our
scheme is demonstrated on recent IBM Quantum devices, producing a model for a
6-qubit state's measurement outcomes with a predictive accuracy (classical
fidelity) > 95% for all test cases using only 100 random measurement settings
as opposed to the 729 settings required for standard full tomography using
local measurements. This reduction in the required number of measurements
scales favourably, with training data in 200 measurement settings yielding a
predictive accuracy > 92% for a 10 qubit state where 59,049 settings are
typically required for full local measurement-based quantum state tomography. A
reduction in number of measurements by a factor, in this case, of almost 600
could allow for estimations of expectation values and state fidelities in
practicable times on current quantum devices. | [
"Alistair W. R. Smith",
"Johnnie Gray",
"M. S. Kim"
] | [
"IBM"
] | "2020-09-16T11:01:00Z" | 2009.07601v3 |
Design of a Quantum-Repeater using Quantum-Circuits and benchmarking its
performance on an IBM Quantum-Computer | Quantum communication relies on the existence of entanglement between two
nodes of a network. However, due to its fragile nature, it is nearly impossible
to establish entanglement at large distances through the direct transmission of
qubits. Quantum repeaters have been proposed to solve this problem, which
split-up the network to create small-scale entangled links and then connect
them up to create the large-scale link. As researchers race to establish
entanglement over larger and larger distances, it becomes essential to gauge
the performance and robustness of the different protocols that have been
proposed to design a quantum repeater, before deploying them in real life.
Currently available noisy quantum computers are ideal for this task, as they
can emulate the noisy environment in a quantum communication channel, and
provide a measure for how the protocols will perform on real-life hardware. In
this paper, we report the circuit-level implementation of the complete
architecture of a quantum repeater, and benchmark this protocol on IBM's cloud
quantum computer - IBMQ. Our experiments indicate a 26% fidelity of shared
bell-pairs for a complete on-chip quantum repeater with a yield of 49%. We also
compare these results with simulation data from IBM Qiskit. The results of our
experiments provide a quantitative measure for the fidelity of entanglement
that currently available repeaters can establish. In addition, the proposed
circuit-implementation provides a robust benchmark for state-of-the-art quantum
computing hardware. | [
"Sowmitra Das",
"Md. Saifur Rahman",
"Mahbub Majumdar"
] | [
"IBM"
] | "2020-09-09T21:44:11Z" | 2009.04584v2 |
Enhancing Fidelity of Quantum Cryptography using Maximally Entangled
Qubits | Securing information transmission is critical today. However, with rapidly
developing powerful quantum technologies, conventional cryptography techniques
are becoming more prone to attacks each day. New techniques in the realm of
quantum cryptography to preserve security against powerful attacks are slowly
emerging. What is important though now is the fidelity of the cryptography,
because security with massive processing power is not worth much if it is not
correct. Focusing on this issue, we propose a method to enhance the fidelity of
quantum cryptography using maximally entangled qubit pairs. For doing so, we
created a graph state along a path consisting of all the qubits of ibmqx4 and
ibmq_16_melbourne respectively and we measure the strength of the entanglement
using negativity measurement of the qubit pairs. Then, using the qubits with
maximal entanglement, we send the modified encryption key to the receiver. The
key is modified by permutation and superdense coding before transmission. The
receiver reverts the process and gets the actual key. We carried out the
complete experiment in the IBM Quantum Experience project. Our result shows a
15% to 20% higher fidelity of encryption and decryption than a random selection
of qubits. | [
"Saiful Islam Salim",
"Adnan Quaium",
"Sriram Chellappan",
"A. B. M. Alim Al Islam"
] | [
"IBM"
] | "2020-09-09T08:12:18Z" | 2009.04155v1 |
Quantum Computation of Finite-Temperature Static and Dynamical
Properties of Spin Systems Using Quantum Imaginary Time Evolution | Developing scalable quantum algorithms to study finite-temperature physics of
quantum many-body systems has attracted considerable interest due to recent
advancements in quantum hardware. However, such algorithms in their present
form require resources that exceed the capabilities of current quantum
computers except for a limited range of system sizes and observables. Here, we
report calculations of finite-temperature properties including energies, static
and dynamical correlation functions, and excitation spectra of spin
Hamiltonians with up to four sites on five-qubit IBM Quantum devices. These
calculations are performed using the quantum imaginary time evolution (QITE)
algorithm and made possible by several algorithmic improvements, including a
method to exploit symmetries that reduces the quantum resources required by
QITE, circuit optimization procedures to reduce circuit depth, and error
mitigation techniques to improve the quality of raw hardware data. Our work
demonstrates that the ansatz-independent QITE algorithm is capable of computing
diverse finite-temperature observables on near-term quantum devices. | [
"Shi-Ning Sun",
"Mario Motta",
"Ruslan N. Tazhigulov",
"Adrian T. K. Tan",
"Garnet Kin-Lic Chan",
"Austin J. Minnich"
] | [
"IBM"
] | "2020-09-08T06:49:08Z" | 2009.03542v1 |
SlackQ : Approaching the Qubit Mapping Problem with A Slack-aware Swap
Insertion Scheme | The rapid progress of physical implementation of quantum computers paved the
way for the design of tools to help users write quantum programs for any given
quantum device. The physical constraints inherent in current NISQ architectures
prevent most quantum algorithms from being directly executed on quantum
devices. To enable two-qubit gates in the algorithm, existing works focus on
inserting SWAP gates to dynamically remap logical qubits to physical qubits.
However, their schemes lack consideration of the execution time of generated
quantum circuits. In this work, we propose a slack-aware SWAP insertion scheme
for the qubit mapping problem in the NISQ era. Our experiments show performance
improvement by up to 2.36X at maximum, by 1.62X on average, over 106
representative benchmarks from RevLib, IBM Qiskit , and ScaffCC. | [
"Chi Zhang",
"Yanhao Chen",
"Yuwei Jin",
"Wonsun Ahn",
"Youtao Zhang",
"Eddy Z. Zhang"
] | [
"IBM"
] | "2020-09-04T18:12:54Z" | 2009.02346v1 |
Asymmetry of CNOT gate operation in superconducting transmon quantum
processors using cross-resonance entangling | Controlled-NOT (CNOT) gates are commonly included in the standard gate set of
quantum processors and provide an important way to entangle qubits. For
fixed-frequency qubits using the cross-resonance entangling technique, using
the higher-frequency qubit to control the lower-frequency qubit enables much
shorter entangling times than using the lower-frequency qubit as the control.
Consequently, when implementing a CNOT gate where logical control by the
lower-frequency qubit is needed, compilers may implement this functionality by
using an equivalent circuit such as placing Hadamard gates on both qubits
before and after a CNOT gate controlled by the higher-frequency qubit. However,
since the implementation is different depending on which qubit is the control,
a natural question arises regarding the relative performance of the
implementations. We have explored this using quantum processors on the IBM Q
network. The basic circuit used consisted of operations to create a Bell State,
followed by the inverse operations so as to return the qubits to their initial
state in the absence of errors (Hadamard + CNOT + barrier + CNOT + Hadamard).
The circuit depth was varied using multiples of this basic circuit. An
asymmetry in the error of the final state was observed that increased with the
circuit depth. The strength and direction of the asymmetry was unique but
repeatable for each pair of coupled qubits tested. This observation suggests
that the asymmetry in CNOT implementation should be characterized for the
qubits of interest and incorporated into circuit transpilation to obtain the
best accuracy for a particular computation. | [
"Travis Hurant",
"Daniel D. Stancil"
] | [
"IBM"
] | "2020-09-02T20:42:27Z" | 2009.01333v1 |
Simulation of non-radiative energy transfer in photosynthetic systems
using a quantum computer | Photosynthesis is an important and complex physical process in nature, whose
comprehensive understanding would have many relevant industrial applications,
for instance in the field of energy production. In this paper we propose a
quantum algorithm for the simulation of the excitonic transport of energy,
occurring in the first stage of the process of photosynthesis. The algorithm
takes in account the quantum and environmental effects (pure-dephasing),
influencing the quantum transport. We performed quantum simulations of such
phenomena, for a proof of concept scenario, in an actual quantum computer the
IBM Q, of 5 qubits. We validate the results with the Haken-Str\"obl model and
discuss the influence of environmental parameters on the efficiency of the
energy transport. | [
"José Diogo Guimarães",
"Carlos Tavares",
"Luís Soares Barbosa",
"Mikhail I. Vasilevskiy"
] | [
"IBM"
] | "2020-09-02T18:27:07Z" | 2009.01283v1 |
Maximal entropy approach for quantum state tomography | Quantum computation has been growing rapidly in both theory and experiments.
In particular, quantum computing devices with a large number of qubits have
been developed by IBM, Google, IonQ, and others. The current quantum computing
devices are noisy intermediate-scale quantum $($NISQ$)$ devices, and so
approaches to validate quantum processing on these quantum devices are needed.
One of the most common ways of validation for an n-qubit quantum system is
quantum tomography, which tries to reconstruct a quantum system's density
matrix by a complete set of observables. However, the inherent noise in the
quantum systems and the intrinsic limitations poses a critical challenge to
precisely know the actual measurement operators which make quantum tomography
impractical in experiments. Here, we propose an alternative approach to quantum
tomography, based on the maximal information entropy, that can predict the
values of unknown observables based on the available mean measurement data.
This can then be used to reconstruct the density matrix with high fidelity even
though the results for some observables are missing. Of additional contexts, a
practical approach to the inference of the quantum mechanical state using only
partial information is also needed. | [
"Rishabh Gupta",
"Rongxin Xia",
"Raphael D. Levine",
"Sabre Kais"
] | [
"IBM"
] | "2020-09-02T04:39:45Z" | 2009.00815v2 |
Realizing highly entangled states in asymmetrically coupled three NV
centers at room temperature | Despite numerous efforts the coupling between randomly arranged multi-NV
centers and also resonators has not been improved significantly mainly due to
our limited knowledge of their entanglement times (2t_ent). Here, we
demonstrate a very strong coupling between three-NV centers by using a
simulated triple electron-electron resonance experiment based on a new quantum
(U_C) gate on IBM quantum simulator with 2t_ent ~12.5 microsecond arranged is a
triangular configuration. Interestingly through breaking the symmetry of
couplings an even lower 2t_ent ~6.3 {\mu}s can be achieved. This simulation not
only explains the luminescence spectra in recently observed three-NV centers
[Haruyama, Nat. Commun. 2019] but also shows a large improvement of the
entanglement in artificially created structures through a cyclic redistribution
of couplings. Realistically disordered coupling configurations of NV centers
qubits with short time periods and high (0.89-0.99) fidelity of states clearly
demonstrate possibility of accurate quantum registers operated at room
temperature. | [
"Declan Mahony",
"Somnath Bhattacharyya"
] | [
"IBM"
] | "2020-09-01T17:02:46Z" | 2009.00570v1 |
Supercomputer simulations of transmon quantum computers | We develop a simulator for quantum computers composed of superconducting
transmon qubits. The simulation model supports an arbitrary number of transmons
and resonators. Quantum gates are implemented by time-dependent pulses.
Nontrivial effects such as crosstalk, leakage to non-computational states,
entanglement between transmons and resonators, and control errors due to the
pulses are inherently included. The time evolution of the quantum computer is
obtained by solving the time-dependent Schr\"odinger equation. The simulation
algorithm shows excellent scalability on high-performance supercomputers. We
present results for the simulation of up to 16 transmons and resonators.
Additionally, the model can be used to simulate environments, and we
demonstrate the transition from an isolated system to an open quantum system
governed by a Lindblad master equation. We also describe a procedure to extract
model parameters from electromagnetic simulations or experiments. We compare
simulation results to experiments on several NISQ processors of the IBM Q
Experience. We find nearly perfect agreement between simulation and experiment
for quantum circuits designed to probe crosstalk in transmon systems. By
studying common gate metrics such as the fidelity or the diamond distance, we
find that they cannot reliably predict the performance of repeated gate
applications or practical quantum algorithms. As an alternative, we find that
the results from two-transmon gate set tomography have an exceptional
predictive power. Finally, we test a protocol from the theory of quantum error
correction and fault tolerance. We find that the protocol systematically
improves the performance of transmon quantum computers in the presence of
characteristic control and measurement errors. | [
"Dennis Willsch"
] | [
"IBM"
] | "2020-08-31T11:07:02Z" | 2008.13490v1 |
Hybrid Quantum-Classical Eigensolver Without Variation or Parametric
Gates | The use of near-term quantum devices that lack quantum error correction, for
addressing quantum chemistry and physics problems, requires hybrid
quantum-classical algorithms and techniques. Here we present a process for
obtaining the eigenenergy spectrum of electronic quantum systems. This is
achieved by projecting the Hamiltonian of a quantum system onto a limited
effective Hilbert space specified by a set of computational bases. From this
projection an effective Hamiltonian is obtained. Furthermore, a process for
preparing short depth quantum circuits to measure the corresponding diagonal
and off-diagonal terms of the effective Hamiltonian is given, whereby quantum
entanglement and ancilla qubits are used. The effective Hamiltonian is then
diagonalized on a classical computer using numerical algorithms to obtain the
eigenvalues. The use case of this approach is demonstrated for ground sate and
excited states of BeH$_2$ and LiH molecules, and the density of states, which
agrees well with exact solutions. Additionally, hardware demonstration is
presented using IBM quantum devices for H$_2$ molecule. | [
"Pejman Jouzdani",
"Stefan Bringuier"
] | [
"IBM"
] | "2020-08-26T02:31:24Z" | 2008.11347v2 |
Quantum Circuit Transformation: A Monte Carlo Tree Search Framework | In Noisy Intermediate-Scale Quantum (NISQ) era, quantum processing units
(QPUs) suffer from, among others, highly limited connectivity between physical
qubits. To make a quantum circuit effectively executable, a circuit
transformation process is necessary to transform it, with overhead cost the
smaller the better, into a functionally equivalent one so that the connectivity
constraints imposed by the QPU are satisfied. While several algorithms have
been proposed for this goal, the overhead costs are often very high, which
degenerates the fidelity of the obtained circuits sharply. One major reason for
this lies in that, due to the high branching factor and vast search space,
almost all these algorithms only search very shallowly and thus, very often,
only (at most) locally optimal solutions can be reached. In this paper, we
propose a Monte Carlo Tree Search (MCTS) framework to tackle the circuit
transformation problem, which enables the search process to go much deeper. The
general framework supports implementations aiming to reduce either the size or
depth of the output circuit through introducing SWAP or remote CNOT gates. The
algorithms, called MCTS-Size and MCTS-Depth, are polynomial in all relevant
parameters. Empirical results on extensive realistic circuits and IBM Q Tokyo
show that the MCTS-based algorithms can reduce the size (depth, resp.) overhead
by, on average, 66% (84%, resp.) when compared with tket, an industrial level
compiler. | [
"Xiangzhen Zhou",
"Yuan Feng",
"Sanjiang Li"
] | [
"IBM"
] | "2020-08-21T06:54:55Z" | 2008.09331v4 |
Pure State Tomography with Fourier Transformation | Extracting information from quantum devices has long been a crucial problem
in the field of quantum mechanics. By performing elaborate measurements,
quantum state tomography, an important and fundamental tool in quantum science
and technology, can be used to determine unknown quantum states completely. In
this study, we explore methods to determine multi-qubit pure quantum states
uniquely and directly. Two adaptive protocols are proposed, with their
respective quantum circuits. Herein, two or three observables are sufficient,
while the number of measurement outcomes is either the same as or fewer than
those in existing methods. Additionally, experiments on the IBM 5-qubit quantum
computer, as well as numerical investigations, demonstrate the feasibility of
the proposed protocols. | [
"Yu Wang",
"Keren Li"
] | [
"IBM"
] | "2020-08-20T17:13:09Z" | 2008.09079v4 |
Microcanonical and finite temperature ab initio molecular dynamics
simulations on quantum computers | Ab initio molecular dynamics (AIMD) is a powerful tool to predict properties
of molecular and condensed matter systems. The quality of this procedure is
based on accurate electronic structure calculations. The development of quantum
processors has shown great potential for the efficient evaluation of accurate
ground and excited state energies of molecular systems, opening up new avenues
for molecular dynamics simulations. In this work we address the use of
variational quantum algorithms for the calculation of accurate atomic forces to
be used in AIMD. In particular, we provide solutions for the alleviation of the
statistical noise associated to the measurements of the expectation values of
energies and forces, as well as schemes for the mitigation of the hardware
noise sources (in particular, gate infidelities, qubit decoherence and readout
errors). Despite the relative large error in the calculation of the potential
energy, our results show that the proposed algorithms can provide reliable MD
trajectories in the microcanonical (constant energy) ensemble. Further,
exploiting the intrinsic noise arising from the quantum measurement process, we
also propose a Langevin dynamics algorithm for the simulation of canonical,
i.e., constant temperature, dynamics. Both algorithms (microcanonical and
canonical) are applied to the simulation of simple molecular systems such as H2
and H3+. Finally, we also provide results for the dynamics of H2 obtained with
IBM quantum computer ibmq_athens. | [
"Igor O. Sokolov",
"Panagiotis Kl. Barkoutsos",
"Lukas Moeller",
"Philippe Suchsland",
"Guglielmo Mazzola",
"Ivano Tavernelli"
] | [
"IBM"
] | "2020-08-18T20:24:27Z" | 2008.08144v1 |
A novel three party Quantum secret sharing scheme based on Bell state
sequential measurements with application in quantum image sharing | In this work, we present a quantum secret sharing scheme based on Bell state
entanglement and sequential projection measurements. The protocol verifies the
$n$ out of $n$ scheme and supports the aborting of the protocol in case all the
parties do not divulge in their valid measurement outcomes. The operator-qubit
pair forms an integral part of the scheme determining the classical secret to
be shared. The protocol is robust enough to neutralize any eavesdropping on a
particular qubit of the dealer. The experimental demonstration of the scheme is
done on IBM-QE cloud platform with backends \texttt{IBMQ\_16\_Melbourne} and
\texttt{IBMQ\_QASM\_SIMULATOR\_V0.1.547} simulator. The security analysis
performed on the scheme and the comparative analysis supports our claim of a
stringent and an efficient scheme as compared to some recent quantum and
semi-quantum techniques of secret sharing. | [
"Farhan Musanna",
"Sanjeev Kumar"
] | [
"IBM"
] | "2020-08-14T07:50:35Z" | 2008.06228v1 |
Quantifying coherence of quantum measurements | In this work we investigate how to quantify the coherence of quantum
measurements. First, we establish a resource theoretical framework to address
the coherence of measurement and show that any statistical distance can be
adopted to define a coherence monotone of measurement. For instance, the
relative entropy fulfills all the required properties as a proper monotone. We
specifically introduce a coherence monotone of measurement in terms of
off-diagonal elements of Positive-Operator-Valued Measure (POVM) components.
This quantification provides a lower bound on the robustness of
measurement-coherence that has an operational meaning as the maximal advantage
over all incoherent measurements in state discrimination tasks. Finally, we
propose an experimental scheme to assess our quantification of
measurement-coherence and demonstrate it by performing an experiment using a
single qubit on IBM Q processor. | [
"Kyunghyun Baek",
"Adel Sohbi",
"Jaehak Lee",
"Jaewan Kim",
"Hyunchul Nha"
] | [
"IBM"
] | "2020-08-10T09:57:28Z" | 2008.03999v1 |
Faster Schrödinger-style simulation of quantum circuits | Recent demonstrations of superconducting quantum computers by Google and IBM
and trapped-ion computers from IonQ fueled new research in quantum algorithms,
compilation into quantum circuits, and empirical algorithmics. While online
access to quantum hardware remains too limited to meet the demand, simulating
quantum circuits on conventional computers satisfies many needs. We advance
Schr\"odinger-style simulation of quantum circuits that is useful standalone
and as a building block in layered simulation algorithms, both cases are
illustrated in our results. Our algorithmic contributions show how to simulate
multiple quantum gates at once, how to avoid floating-point multiplies, how to
best use instruction-level and thread-level parallelism as well as CPU cache,
and how to leverage these optimizations by reordering circuit gates. While not
described previously, these techniques implemented by us supported published
high-performance distributed simulations up to 64 qubits. To show additional
impact, we benchmark our simulator against Microsoft, IBM and Google simulators
on hard circuits from Google. | [
"Aneeqa Fatima",
"Igor L. Markov"
] | [
"IBM"
] | "2020-08-01T08:47:24Z" | 2008.00216v3 |
Demonstrating Quantum Zeno Effect on IBM Quantum Experience | Quantum Zeno Effect (QZE) has been one of the most interesting phenomena in
quantum mechanics ever since its discovery in 1977 by Misra and Sudarshan [J.
Math. Phys. \textbf{18}, 756 (1977)]. There have been many attempts for
experimental realization of the same. Here, we present the first ever
simulation of QZE on IBM quantum experience platform. We simulate a two-level
system for Rabi-driven oscillation and then disturb the time evolution by
intermediate repetitive measurements using quantum gates to increase the
survival probability of the qubit in the initial state. The circuits are
designed along with the added intermediate measurements and executed on IBM
quantum simulator, and the outcomes are shown to be consistent with the
predictions. The increasing survival probability with the number of
intermediate measurements demonstrates QZE. Furthermore, some alternative
explanations for the obtained results are provided which leads to some
ambiguity in giving the exact reasoning for the observed outcomes. | [
"Subhashish Barik",
"Dhiman Kumar Kalita",
"Bikash K. Behera",
"Prasanta K. Panigrahi"
] | [
"IBM"
] | "2020-08-01T02:44:53Z" | 2008.01070v1 |
Experimental semi-autonomous eigensolver using reinforcement learning | The characterization of observables, expressed via Hermitian operators, is a
crucial task in quantum mechanics. For this reason, an eigensolver is a
fundamental algorithm for any quantum technology. In this work, we implement a
semi-autonomous algorithm to obtain an approximation of the eigenvectors of an
arbitrary Hermitian operator using the IBM quantum computer. To this end, we
only use single-shot measurements and pseudo-random changes handled by a
feedback loop, reducing the number of measures in the system. Due to the
classical feedback loop, this algorithm can be cast into the reinforcement
learning paradigm. Using this algorithm, for a single-qubit observable, we
obtain both eigenvectors with fidelities over 0.97 with around 200 single-shot
measurements. For two-qubits observables, we get fidelities over 0.91 with
around 1500 single-shot measurements for the four eigenvectors, which is a
comparatively low resource demand, suitable for current devices. This work is
useful to the development of quantum devices able to decide with partial
information, which helps to implement future technologies in quantum artificial
intelligence. | [
"C. -Y. Pan",
"M. Hao",
"N. Barraza",
"E. Solano",
"F. Albarran-Arriagada"
] | [
"IBM"
] | "2020-07-30T15:20:46Z" | 2007.15521v2 |
Experimental implementation of non-Clifford interleaved randomized
benchmarking with a controlled-S gate | Hardware efficient transpilation of quantum circuits to a quantum devices
native gateset is essential for the execution of quantum algorithms on noisy
quantum computers. Typical quantum devices utilize a gateset with a single
two-qubit Clifford entangling gate per pair of coupled qubits, however, in some
applications access to a non-Clifford two-qubit gate can result in more optimal
circuit decompositions and also allows more flexibility in optimizing over
noise. We demonstrate calibration of a low error non-Clifford
Controlled-$\frac{\pi}{2}$ phase (CS) gate on a cloud based IBM Quantum
computing using the Qiskit Pulse framework. To measure the gate error of the
calibrated CS gate we perform non-Clifford CNOT-Dihedral interleaved randomized
benchmarking. We are able to obtain a gate error of $5.9(7) \times 10^{-3}$ at
a gate length 263 ns, which is close to the coherence limit of the associated
qubits, and lower error than the backends standard calibrated CNOT gate. | [
"Shelly Garion",
"Naoki Kanazawa",
"Haggai Landa",
"David C. McKay",
"Sarah Sheldon",
"Andrew W. Cross",
"Christopher J. Wood"
] | [
"IBM"
] | "2020-07-16T18:00:02Z" | 2007.08532v2 |
A non-algorithmic approach to "programming" quantum computers via
machine learning | Major obstacles remain to the implementation of macroscopic quantum
computing: hardware problems of noise, decoherence, and scaling; software
problems of error correction; and, most important, algorithm construction.
Finding truly quantum algorithms is quite difficult, and many of these genuine
quantum algorithms, like Shor's prime factoring or phase estimation, require
extremely long circuit depth for any practical application, which necessitates
error correction. In contrast, we show that machine learning can be used as a
systematic method to construct algorithms, that is, to non-algorithmically
"program" quantum computers. Quantum machine learning enables us to perform
computations without breaking down an algorithm into its gate "building
blocks", eliminating that difficult step and potentially increasing efficiency
by simplifying and reducing unnecessary complexity. In addition, our
non-algorithmic machine learning approach is robust to both noise and to
decoherence, which is ideal for running on inherently noisy NISQ devices which
are limited in the number of qubits available for error correction. We
demonstrate this using a fundamentally non-classical calculation:
experimentally estimating the entanglement of an unknown quantum state. Results
from this have been successfully ported to the IBM hardware and trained using a
hybrid reinforcement learning method. | [
"Nathan Thompson",
"James Steck",
"Elizabeth Behrman"
] | [
"IBM"
] | "2020-07-16T13:36:21Z" | 2007.08327v1 |
Fast Estimation of Sparse Quantum Noise | As quantum computers approach the fault tolerance threshold, diagnosing and
characterizing the noise on large scale quantum devices is increasingly
important. One of the most important classes of noise channels is the class of
Pauli channels, for reasons of both theoretical tractability and experimental
relevance. Here we present a practical algorithm for estimating the $s$ nonzero
Pauli error rates in an $s$-sparse, $n$-qubit Pauli noise channel, or more
generally the $s$ largest Pauli error rates. The algorithm comes with rigorous
recovery guarantees and uses only $O(n^2)$ measurements, $O(s n^2)$ classical
processing time, and Clifford quantum circuits. We experimentally validate a
heuristic version of the algorithm that uses simplified Clifford circuits on
data from an IBM 14-qubit superconducting device and our open source
implementation. These data show that accurate and precise estimation of the
probability of arbitrary-weight Pauli errors is possible even when the signal
is two orders of magnitude below the measurement noise floor. | [
"Robin Harper",
"Wenjun Yu",
"Steven T. Flammia"
] | [
"IBM"
] | "2020-07-15T18:00:01Z" | 2007.07901v2 |
Experimental implementation of leakage elimination operators | Decoherence-induced leakage errors can potentially damage physical or logical
qubits by coupling them to other system levels. Here we report the first
experimental implementation of Leakage Elimination Operators (LEOs) that aims
to reduce this undermining, and that can be applied alongside universal quantum
computing. Using IBM's cloud quantum computer, we have studied three
potentially applicable examples of subspaces in two- and three-qubit Hilbert
spaces and found that the LEOs significantly suppress leakage. | [
"Beatriz Garcia Markaida",
"Lian-Ao Wu"
] | [
"IBM"
] | "2020-07-09T10:39:15Z" | 2007.04694v1 |
Measurement Error Mitigation in Quantum Computers Through Classical
Bit-Flip Correction | We develop a classical bit-flip correction method to mitigate measurement
errors on quantum computers. This method can be applied to any operator, any
number of qubits, and any realistic bit-flip probability. We first demonstrate
the successful performance of this method by correcting the noisy measurements
of the ground-state energy of the longitudinal Ising model. We then generalize
our results to arbitrary operators and test our method both numerically and
experimentally on IBM quantum hardware. As a result, our correction method
reduces the measurement error on the quantum hardware by up to one order of
magnitude. We finally discuss how to pre-process the method and extend it to
other errors sources beyond measurement errors. For local Hamiltonians, the
overhead costs are polynomial in the number of qubits, even if multi-qubit
correlations are included. | [
"Lena Funcke",
"Tobias Hartung",
"Karl Jansen",
"Stefan Kühn",
"Paolo Stornati",
"Xiaoyang Wang"
] | [
"IBM"
] | "2020-07-07T17:52:12Z" | 2007.03663v3 |
On Actual Preparation of Dicke State on a Quantum Computer | The exact number of CNOT and single qubit gates needed to implement a Quantum
Algorithm in a given architecture is one of the central problems of Quantum
Computation. In this work we study the importance of concise realizations of
Partially defined Unitary Transformations for better circuit construction using
the case study of Dicke State Preparation. The Dicke States $(\left|D^n_k
\right>)$ are an important class of entangled states with uses in many branches
of Quantum Information. In this regard we provide the most efficient
Deterministic Dicke State Preparation Circuit in terms of CNOT and single qubit
gate counts in comparison to existing literature. We further observe that our
improvements also reduce architectural constraints of the circuits. We
implement the circuit for preparing $\left| D^4_2 \right>$ on the "ibmqx2"
machine of the IBM QX service and observe that the error induced due to noise
in the system is lesser in comparison to the existing circuit descriptions. We
conclude by describing the CNOT map of the generic $\left| D^n_k \right>$
preparation circuit and analyze different ways of distributing the CNOT gates
in the circuit and its affect on the induced error. | [
"Chandra Sekhar Mukherjee",
"Subhamoy Maitra",
"Vineet Gaurav",
"Dibyendu Roy"
] | [
"IBM"
] | "2020-07-03T13:40:32Z" | 2007.01681v2 |
Realizing Quantum Algorithms on Real Quantum Computing Devices | Quantum computing is currently moving from an academic idea to a practical
reality. Quantum computing in the cloud is already available and allows users
from all over the world to develop and execute real quantum algorithms.
However, companies which are heavily investing in this new technology such as
Google, IBM, Rigetti, Intel, IonQ, and Xanadu follow diverse technological
approaches. This led to a situation where we have substantially different
quantum computing devices available thus far. They mostly differ in the number
and kind of qubits and the connectivity between them. Because of that, various
methods for realizing the intended quantum functionality on a given quantum
computing device are available. This paper provides an introduction and
overview into this domain and describes corresponding methods, also referred to
as compilers, mappers, synthesizers, transpilers, or routers. | [
"Carmen G. Almudever",
"Lingling Lao",
"Robert Wille",
"Gian Giacomo Guerreschi"
] | [
"IBM",
"Rigetti"
] | "2020-07-02T10:23:35Z" | 2007.01000v1 |
Mitigating measurement errors in multi-qubit experiments | Reducing measurement errors in multi-qubit quantum devices is critical for
performing any quantum algorithm. Here we show how to mitigate measurement
errors by a classical post-processing of the measured outcomes. Our techniques
apply to any experiment where measurement outcomes are used for computing
expected values of observables. Two error mitigation schemes are presented
based on tensor product and correlated Markovian noise models. Error rates
parameterizing these noise models can be extracted from the measurement
calibration data using a simple formula. Error mitigation is achieved by
applying the inverse noise matrix to a probability vector that represents the
outcomes of a noisy measurement. The error mitigation overhead, including the
the number of measurements and the cost of the classical post-processing, is
exponential in $\epsilon n$, where $\epsilon$ is the maximum error rate and $n$
is the number of qubits. We report experimental demonstration of our error
mitigation methods on IBM Quantum devices using stabilizer measurements for
graph states with $n\le 12$ qubits and entangled 20-qubit states generated by
low-depth random Clifford circuits. | [
"Sergey Bravyi",
"Sarah Sheldon",
"Abhinav Kandala",
"David C. Mckay",
"Jay M. Gambetta"
] | [
"IBM"
] | "2020-06-24T20:56:18Z" | 2006.14044v2 |
Bell inequality violation on small NISQ computers | Quantum computational experiments exploiting Noisy Intermediate-Scale Quantum
(NISQ) devices to demonstrate violation of a Bell inequality are proposed. They
consist of running specified quantum algorithms on few-qubit computers. If such
a device assures entanglement and performs single-shot measurements, the
detection loophole is avoided. Four concise quantum circuits determining the
expectation values of the relevant observables are used for a two-qubit system.
It is possible to add an ancilla qubit to these circuits and eventually only
measure the ancilla to obtain the relevant information. For a four-qubit NISQ
computer, two algorithms yielding the same averages, however also guaranteeing
a random choice of the observable, are developed. A freedom-of-choice loophole
is therefore avoided. Including an additional ancilla reduces the number of
measurements by one since in this case only the ancillas need to be measured.
Note that these methods, using the NISQ device, are intrinsically quantum
mechanical. Locality loopholes cannot be excluded on present NISQ systems.
Results of simulations on the QX simulator of Quantum Inspire are presented.
The Bell inequality is indeed found to be violated, even if some additional
noise is included by means of the depolarizing channel error model. The
algorithms have been implemented on the IBM Q Experience as well. The results
of these quantum computations support a violation of the Bell inequality by
various standard deviations. | [
"H. W. L. Naus",
"H. Polinder"
] | [
"IBM"
] | "2020-06-24T15:07:39Z" | 2006.13794v2 |
Prospect of using Grover's search in the noisy-intermediate-scale
quantum-computer era | In order to understand the bounds of utilization of the Grover's search
algorithm for the large unstructured data in presence of the quantum computer
noise, we undertake a series of simulations by inflicting various types of
noise, modelled by the IBM QISKit. We apply three forms of Grover's algorithms:
(1) the standard one, with 4-10 qubits, (2) recently published modified
Grover's algorithm, set to reduce the circuit depth, and (3) the algorithms in
(1) and (2) with multi-control Toffoli's modified by addition of an ancilla
qubit. Based on these simulations, we find the upper bound of noise for these
cases, establish its dependence on the quantum depth of the circuit and provide
comparison among them. By extrapolation of the fitted thresholds, we predict
what would be the typical gate error bounds when apply the Grover's algorithms
for the search of a data in a data set as large as thirty two thousands. | [
"Yulun Wang",
"Predrag S. Krstic"
] | [
"IBM"
] | "2020-06-17T17:57:48Z" | 2006.10037v2 |
Determining quantum phase diagrams of topological Kitaev-inspired models
on NISQ quantum hardware | Topological protection is employed in fault-tolerant error correction and in
developing quantum algorithms with topological qubits. But, topological
protection intrinsic to models being simulated, also robustly protects
calculations, even on NISQ hardware. We leverage it by simulating
Kitaev-inspired models on IBM quantum computers and accurately determining
their phase diagrams. This requires constructing conventional quantum circuits
for Majorana braiding to prepare the ground states of Kitaev-inspired models.
The entanglement entropy is then measured to calculate the quantum phase
boundaries. We show how maintaining particle-hole symmetry when sampling
through the Brillouin zone is critical to obtaining high accuracy. This work
illustrates how topological protection intrinsic to a quantum model can be
employed to perform robust calculations on NISQ hardware, when one measures the
appropriate protected quantum properties. It opens the door for further
simulation of topological quantum models on quantum hardware available today. | [
"Xiao Xiao",
"J. K. Freericks",
"A. F. Kemper"
] | [
"IBM"
] | "2020-06-09T21:43:47Z" | 2006.05524v3 |
Estimation of pure states using three measurement bases | We introduce a new method to estimate unknown pure $d$-dimensional quantum
states using the probability distributions associated with only three
measurement bases. Measurement results of $2d$ projectors are employed to
generate a set of $2^{d-1}$ possible states, the likelihood of which is
evaluated using the measurement results of the $d$ remaining projectors. The
state with the highest likelihood is the estimate of the unknown state. The
method estimates all pure states but a null-measure set. The viability of the
protocol is experimentally demonstrated using two different and complementary
high-dimensional quantum information platforms. First, by exploring the
photonic path-encoding strategy, we validate the method on a single
8-dimensional quantum system. Then, we resort to the five superconducting qubit
IBM quantum processor to demonstrate the high performance of the method in the
multipartite scenario. | [
"L. Zambrano",
"L. Pereira",
"D. Martínez",
"G. Cañas",
"G. Lima",
"A. Delgado"
] | [
"IBM"
] | "2020-06-05T03:28:51Z" | 2006.03219v1 |
Quantum Simulation of Nuclear Inelastic Scattering | We present a time-dependent quantum algorithm for nuclear inelastic
scattering in the time-dependent basis function on qubits approach. This
algorithm aims to quantum simulate a subset of the nuclear inelastic scattering
problems that are of physical interest, in which the internal degrees of
freedom of the reaction system are excited by time-dependent external
interactions. We expect that our algorithm will enable an exponential speedup
in simulating the dynamics of the subset of the inelastic scattering problems,
which would also be advantageous for the applications to more complicated
scattering problems. For a demonstration problem, we solve for the Coulomb
excitation of the deuteron, where the quantum simulations are performed with
IBM Qiskit. | [
"Weijie Du",
"James P. Vary",
"Xingbo Zhao",
"Wei Zuo"
] | [
"IBM"
] | "2020-06-02T03:45:11Z" | 2006.01369v4 |
Quantum Divide and Compute: Hardware Demonstrations and Noisy
Simulations | Noisy, intermediate-scale quantum computers come with intrinsic limitations
in terms of the number of qubits (circuit "width") and decoherence time
(circuit "depth") they can have. Here, for the first time, we demonstrate a
recently introduced method that breaks a circuit into smaller subcircuits or
fragments, and thus makes it possible to run circuits that are either too wide
or too deep for a given quantum processor. We investigate the behavior of the
method on one of IBM's 20-qubit superconducting quantum processors with various
numbers of qubits and fragments. We build noise models that capture
decoherence, readout error, and gate imperfections for this particular
processor. We then carry out noisy simulations of the method in order to
account for the observed experimental results. We find an agreement within 20%
between the experimental and the simulated success probabilities, and we
observe that recombining noisy fragments yields overall results that can
outperform the results without fragmentation. | [
"Thomas Ayral",
"François-Marie Le Régent",
"Zain Saleem",
"Yuri Alexeev",
"Martin Suchara"
] | [
"IBM"
] | "2020-05-26T17:08:13Z" | 2005.12874v1 |
Just-in-time Quantum Circuit Transpilation Reduces Noise | Running quantum programs is fraught with challenges on on today's noisy
intermediate scale quantum (NISQ) devices. Many of these challenges originate
from the error characteristics that stem from rapid decoherence and noise
during measurement, qubit connections, crosstalk, the qubits themselves, and
transformations of qubit state via gates. Not only are qubits not "created
equal", but their noise level also changes over time. IBM is said to calibrate
their quantum systems once per day and reports noise levels (errors) at the
time of such calibration. This information is subsequently used to map circuits
to higher quality qubits and connections up to the next calibration point.
This work provides evidence that there is room for improvement over this
daily calibration cycle. It contributes a technique to measure noise levels
(errors) related to qubits immediately before executing one or more sensitive
circuits and shows that just-in-time noise measurements benefit late physical
qubit mappings. With this just-in-time recalibrated transpilation, the fidelity
of results is improved over IBM's default mappings, which only uses their daily
calibrations. The framework assess two major sources of noise, namely readout
errors (measurement errors) and two-qubit gate/connection errors. Experiments
indicate that the accuracy of circuit results improves by 3-304% on average and
up to 400% with on-the-fly circuit mappings based on error measurements just
prior to application execution. | [
"Ellis Wilson",
"Sudhakar Singh",
"Frank Mueller"
] | [
"IBM"
] | "2020-05-26T15:55:36Z" | 2005.12820v1 |
Noise Mitigation with Delay Pulses in the IBM Quantum Experience | One of the greatest challenges for current quantum computing hardware is how
to obtain reliable results from noisy devices. A recent paper [A. Kandala et
al., Nature 567, 491 (2019)] described a method for injecting noise by
stretching gate times, enabling the calculation of quantum expectation values
as a function of the amount of noise in the IBM-Q devices. Extrapolating to
zero noise led to excellent agreement with exact results. Here an alternative
scheme is described that employs the intentional addition of identity pulses,
pausing the device periodically in order to gradually subject the quantum
computation to increased levels of noise. The scheme is implemented in a one
qubit circuit on an IBM-Q device. It is determined that this is an effective
method for controlled addition of noise, and further, that using noisy results
to perform extrapolation can lead to improvements in the final output, provided
careful attention is paid to how the extrapolation is carried out. | [
"Sam Tomkins",
"Rogério de Sousa"
] | [
"IBM"
] | "2020-05-26T05:37:00Z" | 2005.12520v1 |
Mermin's Inequalities of Multiple qubits with Orthogonal Measurements on
IBM Q 53-qubit system | Entanglement properties of IBM Q 53 qubit quantum computer are carefully
examined with the noisy intermediate-scale quantum (NISQ) technology. We study
GHZ-like states with multiple qubits (N=2 to N=7) on IBM Rochester and compare
their maximal violation values of Mermin polynomials with analytic results. A
rule of N-qubits orthogonal measurements is taken to further justify the
entanglement less than maximal values of local realism (LR). The orthogonality
of measurements is another reliable criterion for entanglement except the
maximal values of LR. Our results indicate that the entanglement of IBM
53-qubits is reasonably good when N <= 4 while for the longer entangle chains
the entanglement is only valid for some special connectivity. | [
"Wei-Jia Huang",
"Wei-Chen Chien",
"Chien-Hung Cho",
"Che-Chun Huang",
"Tsung-Wei Huang",
"Ching-Ray Chang"
] | [
"IBM"
] | "2020-05-26T03:34:18Z" | 2005.12504v2 |
Revisiting the experimental test of Mermin's inequalities at IBMQ | Bell-type inequalities allow for experimental testing of local hidden
variable theories. In the present work we show the violation of Mermin's
inequalities in IBM's five-qubit quantum computers, ruling out the local
realism hypothesis in quantum mechanics. Furthermore, our numerical results
show significant improvement with respect to previous implementations. The
circuit implementation of these inequalities is also proposed as a way of
assessing the reliability of different quantum computers. | [
"Diego González",
"Diego Fernández de la Pradilla",
"Guillermo González"
] | [
"IBM"
] | "2020-05-22T16:58:57Z" | 2005.11271v3 |
Quantum computation of lowest-energy Kramers states and magnetic
g-factors of rare earth ions in crystals | We present the results of the quantum calculation of the ground state
energies and magnetic g-factors of two rare earth (RE) ions: Yb3+ in Y2Ti2O7
crystal and Er3+ in YPO4 crystal. The Variational Quantum Eigensolver (VQE)
algorithm has been performed on 5-qubit IBM superconducting quantum computer
via IBM Quantum Experience cloud access. The Hamiltonian of the lowest
spectroscopic multiplet of each RE ion, containing crystal field and Zeeman
interaction, has been projected to the collective states of three (Yb3+) and
four (Er3+) coupled transmon qubits. The lowest-energy states of RE ions have
been found minimizing the mean energy in ~ 250 iterations of the algorithm: the
first part performed on a quantum simulator, and the last 25 iterations - on
the real quantum computing hardware. All the calculated ground-state energies
and magnetic g-factors agree well with their exact values, while the estimated
error of 2{\div}15% is mostly attributed to the decoherence associated with the
two-qubit operations. | [
"K. M. Makushin",
"E. I. Baibekov"
] | [
"IBM"
] | "2020-05-07T19:05:01Z" | 2005.03712v2 |
Interaction-free measurements and counterfactual computation in IBM
quantum computers | The possibility of interaction-free measurements and counterfactual
computations is a striking feature of quantum mechanics pointed out around 20
years ago. We implement such phenomena in actual 5-qubit, 15-qubit and 20-qubit
IBM quantum computers by means of simple quantum circuits. The results are in
general close to the theoretical expectations. For the larger circuits (with
numerous gates and consequently larger errors) we implement a simple error
mitigation procedure which improve appreciably the performance. | [
"J. Alberto Casas",
"Bryan Zaldivar"
] | [
"IBM"
] | "2020-05-07T15:15:13Z" | 2005.03547v2 |
Generalization of CNOT-based Discrete Circular Quantum Walk: Simulation
and Effect of Gate Errors | We investigate the counterparts of random walk in universal quantum computing
and their implementation using standard quantum circuits. Quantum walk have
been recently well investigated for traversing graphs with certain oracles. We
focus our study on traversing a 1-D graph, namely a circle, and show how to
implement discrete circular quantum walk in quantum circuits built with
universal CNOT and single quit gates. We review elementary quantum gates and
circuit decomposition and propose a a generalized version of the all CNOT based
quantum discrete circular walk. We simulated these circuits on an IBM quantum
supercomputer London IBM-Q with 5 qubits. This quantum computer has non perfect
gates based on superconducting qubits, therefore we analyze the impact of
errors on the fidelity of the Walker circuit. | [
"Iyed Ben Slimen",
"Amor Gueddana",
"Vasudevan Lakshminarayanan"
] | [
"IBM"
] | "2020-05-05T19:21:58Z" | 2005.02447v1 |
Satellite quantum repeaters for a quantum Internet | This work presents a satellite alternative to quantum repeaters based on the
terrestrial laid of optical fiber, where the latter have the following
disadvantages: a propagation speed (v) equal to 2/3 of the speed of light (c),
losses and an attenuation in the material that requires the installation of a
repeater every 50 km, while satellite repeaters can cover greater distances at
a speed v = c, with less attenuation and losses than in the case of optical
fiber except for relative environmental aspects to the ground-sky link, i.e.,
clouds that can disrupt the distribution of entangled photons. Two
configurations are presented, the first one of a satellite and the second one
of two satellites in the event that both points on the ground cannot access the
same satellite. Finally, a series of implementations for evaluating the
performance and robustness of both configurations are implemented on a 5 qubits
IBM Q processor. | [
"Sundaraja Sitharama Iyengar",
"Mario Mastriani"
] | [
"IBM"
] | "2020-05-04T15:43:40Z" | 2005.03450v2 |
Preparation of an Exciton Condensate of Photons on a 53-Qubit Quantum
Computer | Quantum computation promises an exponential speedup of certain classes of
classical calculations through the preparation and manipulation of entangled
quantum states. So far most molecular simulations on quantum computers,
however, have been limited to small numbers of particles. Here we prepare a
highly entangled state on a 53-qubit IBM quantum computer, representing 53
particles, which reveals the formation of an exciton condensate of photon
particles and holes. While elusive for more than 50 years, such condensates
were recently achieved for electron-hole pairs in graphene bilayers and metal
chalcogenides. Our result with a photon condensate has the potential to further
the exploration of this new form of condensate that may play a significant role
in realizing efficient room-temperature energy transport. | [
"LeeAnn M. Sager",
"Scott E. Smart",
"David A. Mazziotti"
] | [
"IBM"
] | "2020-04-28T22:02:59Z" | 2004.13868v1 |
Optimized Quantum Compilation for Near-Term Algorithms with OpenPulse | Quantum computers are traditionally operated by programmers at the
granularity of a gate-based instruction set. However, the actual device-level
control of a quantum computer is performed via analog pulses. We introduce a
compiler that exploits direct control at this microarchitectural level to
achieve significant improvements for quantum programs. Unlike quantum optimal
control, our approach is bootstrapped from existing gate calibrations and the
resulting pulses are simple. Our techniques are applicable to any quantum
computer and realizable on current devices. We validate our techniques with
millions of experimental shots on IBM quantum computers, controlled via the
OpenPulse control interface. For representative benchmarks, our pulse control
techniques achieve both 1.6x lower error rates and 2x faster execution time,
relative to standard gate-based compilation. These improvements are critical in
the near-term era of quantum computing, which is bottlenecked by error rates
and qubit lifetimes. | [
"Pranav Gokhale",
"Ali Javadi-Abhari",
"Nathan Earnest",
"Yunong Shi",
"Frederic T. Chong"
] | [
"IBM"
] | "2020-04-23T14:57:00Z" | 2004.11205v2 |
Benchmarking near-term devices with quantum error correction | Now that ever more sophisticated devices for quantum computing are being
developed, we require ever more sophisticated benchmarks. This includes a need
to determine how well these devices support the techniques required for quantum
error correction. In this paper we introduce the \texttt{topological\_codes}
module of Qiskit-Ignis, which is designed to provide the tools necessary to
perform such tests. Specifically, we use the \texttt{RepetitionCode} and
\texttt{GraphDecoder} classes to run tests based on the repetition code and
process the results. As an example, data from a 43 qubit code running on IBM's
\emph{Rochester} device is presented. | [
"James R. Wootton"
] | [
"IBM"
] | "2020-04-23T09:24:23Z" | 2004.11037v1 |
Characterizing the memory capacity of transmon qubit reservoirs | Quantum Reservoir Computing (QRC) exploits the dynamics of quantum ensemble
systems for machine learning. Numerical experiments show that quantum systems
consisting of 5-7 qubits possess computational capabilities comparable to
conventional recurrent neural networks of 100 to 500 nodes. Unlike traditional
neural networks, we do not understand the guiding principles of reservoir
design for high-performance information processing. Understanding the memory
capacity of quantum reservoirs continues to be an open question. In this study,
we focus on the task of characterizing the memory capacity of quantum
reservoirs built using transmon devices provided by IBM. Our hybrid reservoir
achieved a Normalized Mean Square Error (NMSE) of 6x10^{-4} which is comparable
to recent benchmarks. The Memory Capacity characterization of a n-qubit
reservoir showed a systematic variation with the complexity of the topology and
exhibited a peak for the configuration with n-1 self-loops. Such a peak
provides a basis for selecting the optimal design for forecasting tasks. | [
"Samudra Dasgupta",
"Kathleen E. Hamilton",
"Arnab Banerjee"
] | [
"IBM"
] | "2020-04-15T21:21:36Z" | 2004.08240v7 |
Qubit Mapping Based on Subgraph Isomorphism and Filtered Depth-Limited
Search | Mapping logical quantum circuits to Noisy Intermediate-Scale Quantum (NISQ)
devices is a challenging problem which has attracted rapidly increasing
interests from both quantum and classical computing communities. This paper
proposes an efficient method by (i) selecting an initial mapping that takes
into consideration the similarity between the architecture graph of the given
NISQ device and a graph induced by the input logical circuit; and (ii)
searching, in a filtered and depth-limited way, a most useful SWAP combination
that makes executable as many as possible two-qubit gates in the logical
circuit. The proposed circuit transformation algorithm can significantly
decrease the number of auxiliary two-qubit gates required to be added to the
logical circuit, especially when it has a large number of two-qubit gates. For
an extensive benchmark set of 131 circuits and IBM's current premium Q system,
viz., IBM Q Tokyo, our algorithm needs, in average, 0.4346 extra two-qubit
gates per input two-qubit gate, while the corresponding figures for three
state-of-the-art algorithms are 0.6047, 0.8154, and 1.0067 respectively. | [
"Sanjiang Li",
"Xiangzhen Zhou",
"Yuan Feng"
] | [
"IBM"
] | "2020-04-15T15:07:49Z" | 2004.07138v3 |
Qiskit Pulse: Programming Quantum Computers Through the Cloud with
Pulses | The quantum circuit model is an abstraction that hides the underlying
physical implementation of gates and measurements on a quantum computer. For
precise control of real quantum hardware, the ability to execute pulse and
readout-level instructions is required. To that end, we introduce Qiskit Pulse,
a pulse-level programming paradigm implemented as a module within Qiskit-Terra
\cite{Qiskit}. To demonstrate the capabilities of Qiskit Pulse, we calibrate
both un-echoed and echoed variants of the cross-resonance entangling gate with
a pair of qubits on an IBM Quantum system accessible through the cloud. We
perform Hamiltonian characterization of both single and two-pulse variants of
the cross-resonance entangling gate with varying amplitudes on a cloud-based
IBM Quantum system. We then transform these calibrated sequences into a
high-fidelity CNOT gate by applying pre and post local-rotations to the qubits,
achieving average gate fidelities of $F=0.981$ and $F=0.979$ for the un-echoed
and echoed respectively. This is comparable to the standard backend CNOT
fidelity of $F_{CX}=0.984$. Furthermore, to illustrate how users can access
their results at different levels of the readout chain, we build a custom
discriminator to investigate qubit readout correlations. Qiskit Pulse allows
users to explore advanced control schemes such as optimal control theory,
dynamical decoupling, and error mitigation that are not available within the
circuit model. | [
"Thomas Alexander",
"Naoki Kanazawa",
"Daniel J. Egger",
"Lauren Capelluto",
"Christopher J. Wood",
"Ali Javadi-Abhari",
"David McKay"
] | [
"IBM"
] | "2020-04-14T19:03:29Z" | 2004.06755v1 |
Practical numerical integration on NISQ devices | This paper addresses the practical aspects of quantum algorithms used in
numerical integration, specifically their implementation on Noisy
Intermediate-Scale Quantum (NISQ) devices. Quantum algorithms for numerical
integration utilize Quantum Amplitude Estimation (QAE) (Brassard et al., 2002)
in conjunction with Grovers algorithm. However, QAE is daunting to implement on
NISQ devices since it typically relies on Quantum Phase Estimation (QPE), which
requires many ancilla qubits and controlled operations. To mitigate these
challenges, a recently published QAE algorithm (Suzuki et al., 2020), which
does not rely on QPE, requires a much smaller number of controlled operations
and does not require ancilla qubits. We implement this new algorithm for
numerical integration on IBM quantum devices using Qiskit and optimize the
circuit on each target device. We discuss the application of this algorithm on
two qubits and its scalability to more than two qubits on NISQ devices. | [
"Kwangmin Yu",
"Hyunkyung Lim",
"Pooja Rao"
] | [
"IBM"
] | "2020-04-13T01:45:20Z" | 2004.05739v2 |
Towards Dynamic Simulations of Materials on Quantum Computers | A highly anticipated application for quantum computers is as a universal
simulator of quantum many-body systems, as was conjectured by Richard Feynman
in the 1980s. The last decade has witnessed the growing success of quantum
computing for simulating static properties of quantum systems, i.e., the ground
state energy of small molecules. However, it remains a challenge to simulate
quantum many-body dynamics on current-to-near-future noisy intermediate-scale
quantum computers. Here, we demonstrate successful simulation of nontrivial
quantum dynamics on IBM's Q16 Melbourne quantum processor and Rigetti's Aspen
quantum processor; namely, ultrafast control of emergent magnetism by THz
radiation in an atomically-thin two-dimensional material. The full code and
step-by-step tutorials for performing such simulations are included to lower
the barrier to access for future research on these two quantum computers. As
such, this work lays a foundation for the promising study of a wide variety of
quantum dynamics on near-future quantum computers, including dynamic
localization of Floquet states and topological protection of qubits in noisy
environments. | [
"Lindsay Bassman",
"Kuang Liu",
"Aravind Krishnamoorthy",
"Thomas Linker",
"Yifan Geng",
"Daniel Shebib",
"Shogo Fukushima",
"Fuyuki Shimojo",
"Rajiv K. Kalia",
"Aiichiro Nakano",
"Priya Vashishta"
] | [
"IBM",
"Rigetti"
] | "2020-04-09T22:27:09Z" | 2004.04836v1 |
Detecting Temporal Correlation via Quantum Random Number Generation | All computing devices, including quantum computers, must exhibit that for a
given input, an output is produced in accordance with the program. The outputs
generated by quantum computers that fulfill these requirements are not
temporally correlated, however. In a quantum-computing device comprising
solid-state qubits such as superconducting qubits, any operation to rest the
qubits to their initial state faces a practical problem. We applied a
statistical analysis to a collection of random numbers output from a 20-qubit
superconducting-qubit cloud quantum computer using the simplest random number
generation scheme. The analysis indicates temporal correlation in the output of
some sequences obtained from the 20 qubits. This temporal correlation is not
related to the relaxation time of each qubit. We conclude that the correlation
could be a result of a systematic error. | [
"Yutaka Shikano",
"Kentaro Tamura",
"Rudy Raymond"
] | [] | "2020-04-03T01:51:20Z" | 2004.01330v1 |
Quantum simulations of a qubit of space | In loop quantum gravity approach to Planck scale physics, quantum geometry is
represented by superposition of the so-called spin network states. In the
recent literature, a class of spin networks promising from the perspective of
quantum simulations of quantum gravitational systems has been studied. In this
case, the spin network states are represented by graphs with four-valent nodes,
and two dimensional intertwiner Hilbert spaces (qubits of space) attached to
them. In this article, construction of quantum circuits for a general
intertwiner qubit is presented. The obtained circuits are simulated on 5-qubit
(Yorktown) and 15-qubit (Melbourne) IBM superconducting quantum computers,
giving satisfactory fidelities. The circuits provide building blocks for
quantum simulations of complex spin networks in the future. Furthermore, a
class of maximally entangled states of spin networks is introduced. As an
example of application, attempts to determine transition amplitudes for a
monopole and a dipole spin networks with the use of superconducting quantum
processor are made. | [
"Grzegorz Czelusta",
"Jakub Mielczarek"
] | [
"IBM"
] | "2020-03-29T19:53:45Z" | 2003.13124v2 |
Simulation of single photon dynamics in coupled cavities through IBM
quantum computer | We design a quantum circuit in IBM quantum computer that mimics the dynamics
of single photon in a coupled cavity system. By suitably choosing the gate
parameters in the quantum circuit, we could transfer an unknown qubit state
between the qubits. The condition for perfect state transfer is obtained by
solving the unitary time dynamics governed by the Hamiltonian of the coupled
cavity system. We then demonstrate the dynamics of entanglement between the
two-qubits and show violation of Bell's inequality in IBM quantum computer. | [
"Nilakantha Meher",
"Bikash K. Behera",
"Prasanta K. Panigrahi"
] | [
"IBM"
] | "2020-03-22T14:35:03Z" | 2003.09910v1 |
Digital Simulation of Topological Matter on Programmable Quantum
Processors | Simulating the topological phases of matter in synthetic quantum simulators
is a topic of considerable interest. Given the universality of digital quantum
simulators, the prospect of digitally simulating exotic topological phases is
greatly enhanced. However, it is still an open question how to realize digital
quantum simulation of topological phases of matter. Here, using common single-
and two-qubit elementary quantum gates, we propose and demonstrate an approach
to design topologically protected quantum circuits on the current generation of
noisy quantum processors where spin-orbital coupling and related topological
matter can be digitally simulated. In particular, a low-depth topological
quantum circuit is performed on both IBM and Rigetti quantum processors. In the
experiments, we not only observe but also distinguish the 0 and $\pi$ energy
topological edge states by measuring qubit excitation distribution at the
output of the circuits. | [
"Feng Mei",
"Qihao Guo",
"Ya-Fei Yu",
"Liantuan Xiao",
"Shi-Liang Zhu",
"Suotang Jia"
] | [
"IBM",
"Rigetti"
] | "2020-03-13T02:32:48Z" | 2003.06086v2 |
Circuit Design for Clique Problem and Its Implementation on Quantum
Computer | Finding cliques in a graph has several applications for its pattern matching
ability. $k$-clique problem, a special case of clique problem, determines
whether an arbitrary graph contains a clique of size $k$, has already been
addressed in quantum domain. A variant of $k$-clique problem that lists all
cliques of size $k$, has also popular modern-day applications. Albeit, the
implementation of such variant of $k$-clique problem in quantum setting still
remains untouched. In this paper, apart from theoretical solution of such
$k$-clique problem, practical quantum gate-based implementation has been
addressed using Grover's algorithm. This approach is further extended to design
circuit for the maximum clique problem in classical-quantum hybrid
architecture. The algorithm automatically generates the circuit for any given
undirected and unweighted graph and any given $k$, which makes our approach
generalized in nature. The proposed approach of solving $k$-clique problem has
exhibited a reduction of qubit cost and circuit depth as compared to the
state-of-the-art approach, for a small $k$ with respect to a large graph. A
framework that can map the automated generated circuit for clique problem to
quantum devices is also proposed. An analysis of the experimental results is
demonstrated using IBM's Qiskit. | [
"Arpita Sanyal",
"Amit Saha",
"Debasri Saha",
"Banani Saha",
"Amlan Chakrabarti"
] | [
"IBM"
] | "2020-03-10T04:29:35Z" | 2004.10596v4 |
Detecting entanglement by the mean value of spin on a quantum computer | We implement a protocol to determine the degree of entanglement between a
qubit and the rest of the system on a quantum computer. The protocol is based
on results obtained in paper [Frydryszak et al. (2017)]. This protocol is
tested on a 5-qubit superconducting quantum processor called ibmq-ourense
provided by the IBM company. We determine the values of entanglement of the
Schr\"odinger cat and the Werner states prepared on this device and compare
them with the theoretical ones. In addition, a protocol for determining the
entanglement of rank-2 mixed states is proposed. We apply this protocol to the
mixed state which consists of two Bell states prepared on the ibmq-ourense
quantum device. | [
"A. R. Kuzmak",
"V. M. Tkachuk"
] | [
"IBM"
] | "2020-03-02T16:39:13Z" | 2003.01011v2 |
Demonstrating NISQ Era Challenges in Algorithm Design on IBM's 20 Qubit
Quantum Computer | As superconducting qubits continue to advance technologically, the
realization of quantum algorithms from theoretical abstraction to physical
implementation requires knowledge of both quantum circuit construction as well
as hardware limitations. In this study we present results from experiments run
on IBM's 20-qubit `Poughkeepsie' architecture, with the goal of demonstrating
various qubit qualities and challenges that arise in designing quantum
algorithms. These include experimentally measuring $T_1$ and $T_2$ coherence
times, gate fidelities, sequential CNOT gates, techniques for handling ancilla
qubits, and finally CCNOT and QFT$^{\dagger}$ circuits implemented on several
different qubit geometries. Our results demonstrate various techniques for
improving quantum circuits which must compensate for limited connectivity,
either through the use of SWAP gates or additional ancilla qubits. | [
"Daniel Koch",
"Brett Martin",
"Saahil Patel",
"Laura Wessing",
"Paul M. Alsing"
] | [
"IBM"
] | "2020-03-02T16:36:33Z" | 2003.01009v3 |
Identification of networking quantum teleportation on 14-qubit IBM
universal quantum computer | Quantum teleportation enables networking participants to move an unknown
quantum state between the nodes of a quantum network, and hence constitutes an
essential element in constructing large-sale quantum processors with a quantum
modular architecture. Herein, we propose two protocols for teleporting qubits
through an N-node quantum network in a highly-entangled box-cluster state or
chain-type cluster state. The proposed protocols are systematically scalable to
an arbitrary finite number N and applicable to arbitrary size of modules. The
protocol based on a box-cluster state is implemented on a 14-qubit IBM quantum
computer for N up to 12. To identify faithful networking teleportation, namely
that the elements on real devices required for the networking teleportation
process are all qualified for achieving teleportation task, we quantify
quantum-mechanical processes using a generic classical-process model through
which any classical strategies of mimicry of teleportation can be ruled out.
From the viewpoint of achieving a genuinely quantum-mechanical process, the
present work provides a novel toolbox consisting of the networking
teleportation protocols and the criteria for identifying faithful teleportation
for universal quantum computers with modular architectures and facilitates
further improvements in the reliability of quantum-information processing. | [
"Ni-Ni Huang",
"Wei-Hao Huang",
"Che-Ming Li"
] | [
"IBM"
] | "2020-02-20T11:02:02Z" | 2002.08671v1 |
Experimental Implementation of Quantum Walks on IBM Quantum Computers | The development of universal quantum computers has achieved remarkable
success in recent years, culminating with the quantum supremacy reported by
Google. Now is possible to implement short-depth quantum circuits with dozens
of qubits and to obtain results with significant fidelity. Quantum walks are
good candidates to be implemented on the available quantum computers. In this
work, we implement discrete-time quantum walks with one and two interacting
walkers on cycles, two-dimensional lattices, and complete graphs on IBM quantum
computers. We are able to obtain meaningful results using the cycle, the
two-dimensional lattice, and the complete graph with 16 nodes each, which
require 4-qubit quantum circuits up to depth 100. | [
"Frank Acasiete",
"Flavia P. Agostini",
"Jalil Khatibi Moqadam",
"Renato Portugal"
] | [
"IBM"
] | "2020-02-05T18:15:36Z" | 2002.01905v3 |
Rigorous measurement error correction | We review an experimental technique used to correct state preparation and
measurement errors on gate-based quantum computers, and discuss its rigorous
justification. Within a specific biased quantum measurement model, we prove
that nonideal measurement of an arbitrary $n$-qubit state is equivalent to
ideal projective measurement followed by a classical Markov process $\Gamma$
acting on the output probability distribution. Measurement errors can be
removed, with rigorous justification, if $\Gamma$ can be learned and inverted.
We show how to obtain $\Gamma$ from gate set tomography (R. Blume-Kohout et
al., arXiv:1310.4492) and apply the error correction technique to single IBM Q
superconducting qubits. | [
"Michael R. Geller"
] | [
"IBM"
] | "2020-02-04T18:58:06Z" | 2002.01471v2 |
Efficient correction of multiqubit measurement errors | State preparation and measurement (SPAM) errors limit the performance of
near-term quantum computers and their potential for practical application. SPAM
errors are partly correctable after a calibration step that requires, for a
complete implementation on a register of $n$ qubits, $2^n$ additional
measurements. Here we introduce an approximate but efficient method for
multiqubit SPAM error characterization and mitigation requiring the classical
processing of $2^n \! \times 2^n$ matrices, but only $O(4^k n^2)$ measurements,
where $k=O(1)$ is the number of qubits in a correlation volume. We demonstrate
and validate the technique using an IBM Q processor on registers of 4 and 8
superconducting qubits. | [
"Michael R. Geller",
"Mingyu Sun"
] | [
"IBM"
] | "2020-01-27T18:57:40Z" | 2001.09980v2 |
Testing a Quantum Error-Correcting Code on Various Platforms | Quantum error correction plays an important role in fault-tolerant quantum
information processing. It is usually difficult to experimentally realize
quantum error correction, as it requires multiple qubits and quantum gates with
high fidelity. Here we propose a simple quantum error-correcting code for the
detected amplitude damping channel. The code requires only two qubits. We
implement the encoding, the channel, and the recovery on an optical platform,
the IBM Q System, and a nuclear magnetic resonance system. For all of these
systems, the error correction advantage appears when the damping rate exceeds
some threshold. We compare the features of these quantum information processing
systems used and demonstrate the advantage of quantum error correction on
current quantum computing platforms. | [
"Qihao Guo",
"Yuan-Yuan Zhao",
"Markus Grassl",
"Xinfang Nie",
"Guo-Yong Xiang",
"Tao Xin",
"Zhang-Qi Yin",
"Bei Zeng"
] | [
"IBM"
] | "2020-01-22T13:15:16Z" | 2001.07998v1 |
Subdivided Phase Oracle for NISQ Search Algorithms | Because noisy, intermediate-scale quantum (NISQ) machines accumulate errors
quickly, we need new approaches to designing NISQ-aware algorithms and
assessing their performance. Algorithms with characteristics that appear less
desirable under ideal circumstances, such as lower success probability, may in
fact outperform their ideal counterparts on existing hardware. We propose an
adaptation of Grover's algorithm, subdividing the phase flip into segments to
replace a digital counter and complex phase flip decision logic. We applied
this approach to obtaining the best solution of the MAX-CUT problem in sparse
graphs, utilizing multi-control, Toffoli-like gates with residual phase shifts.
We implemented this algorithm on IBM Q processors and succeeded in solving a
5-node MAX-CUT problem, demonstrating amplitude amplification on four qubits.
This approach will be useful for a range of problems, and may shorten the time
to reaching quantum advantage. | [
"Takahiko Satoh",
"Yasuhiro Ohkura",
"Rodney Van Meter"
] | [
"IBM"
] | "2020-01-18T01:54:12Z" | 2001.06575v3 |
Software Mitigation of Crosstalk on Noisy Intermediate-Scale Quantum
Computers | Crosstalk is a major source of noise in Noisy Intermediate-Scale Quantum
(NISQ) systems and is a fundamental challenge for hardware design. When
multiple instructions are executed in parallel, crosstalk between the
instructions can corrupt the quantum state and lead to incorrect program
execution. Our goal is to mitigate the application impact of crosstalk noise
through software techniques. This requires (i) accurate characterization of
hardware crosstalk, and (ii) intelligent instruction scheduling to serialize
the affected operations. Since crosstalk characterization is computationally
expensive, we develop optimizations which reduce the characterization overhead.
On three 20-qubit IBMQ systems, we demonstrate two orders of magnitude
reduction in characterization time (compute time on the QC device) compared to
all-pairs crosstalk measurements. Informed by these characterization, we
develop a scheduler that judiciously serializes high crosstalk instructions
balancing the need to mitigate crosstalk and exponential decoherence errors
from serialization. On real-system runs on three IBMQ systems, our scheduler
improves the error rate of application circuits by up to 5.6x, compared to the
IBM instruction scheduler and offers near-optimal crosstalk mitigation in
practice.
In a broader picture, the difficulty of mitigating crosstalk has recently
driven QC vendors to move towards sparser qubit connectivity or disabling
nearby operations entirely in hardware, which can be detrimental to
performance. Our work makes the case for software mitigation of crosstalk
errors. | [
"Prakash Murali",
"David C. McKay",
"Margaret Martonosi",
"Ali Javadi-Abhari"
] | [
"IBM"
] | "2020-01-09T04:00:03Z" | 2001.02826v1 |
Quantum Chemistry Simulations of Dominant Products in Lithium-Sulfur
Batteries | Quantum chemistry simulations of some industrially relevant molecules are
reported, employing variational quantum algorithms for near-term quantum
devices. The energies and dipole moments are calculated along the dissociation
curves for lithium hydride (LiH), hydrogen sulfide, lithium hydrogen sulfide
and lithium sulfide. In all cases we focus on the breaking of a single bond, to
obtain information about the stability of the molecular species being
investigated. We calculate energies and a variety of electrostatic properties
of these molecules using classical simulators of quantum devices, with up to 21
qubits for lithium sulfide. Moreover, we calculate the ground-state energy and
dipole moment along the dissociation pathway of LiH using IBM quantum devices.
This is the first example, to the best of our knowledge, of dipole moment
calculations being performed on quantum hardware. | [
"Julia E. Rice",
"Tanvi P. Gujarati",
"Tyler Y. Takeshita",
"Joe Latone",
"Mario Motta",
"Andreas Hintennach",
"Jeannette M. Garcia"
] | [
"IBM"
] | "2020-01-04T19:52:41Z" | 2001.01120v2 |
Calculation of $π$ on the IBM quantum computer and the accuracy of
one-qubit operations | A quantum algorithm for the calculation of $\pi$ is proposed and implemented
on the five-qubit IBM quantum computer with superconducting qubits. We find
$\pi=3.157\pm0.017$. The error is due to the noise of quantum one-qubit
operations and measurements. The results can be used for estimating the errors
of the quantum computer and suggest that the errors are purely random. | [
"G. A. Bochkin",
"S. I. Doronin",
"E. B. Fel'dman",
"A. I. Zenchuk"
] | [
"IBM"
] | "2019-12-27T09:29:06Z" | 1912.12037v2 |
Driven-dissipative quantum mechanics on a lattice: Simulating a
fermionic reservoir on a quantum computer | The driven-dissipative many-body problem remains one of the most challenging
unsolved problems in quantum mechanics. The advent of quantum computers may
provide a unique platform for efficiently simulating such driven-dissipative
systems. But there are many choices for how one can engineer the reservoir. One
can simply employ ancilla qubits to act as a reservoir and then digitally
simulate them via algorithmic cooling. A more attractive approach, which allows
one to simulate an infinite reservoir, is to integrate out the bath degrees of
freedom and describe the driven-dissipative system via a master equation, that
can also be simulated on a quantum computer. In this work, we consider the
particular case of non-interacting electrons on a lattice driven by an electric
field and coupled to a fermionic thermostat. Then, we provide two different
quantum circuits: the first one reconstructs the full dynamics of the system
using Trotter steps, while the second one dissipatively prepares the final
non-equilibrium steady state in a single step. We run both circuits on the IBM
quantum experience. For circuit (i), we achieved up to 5 Trotter steps. When
partial resets become available on quantum computers, we expect that the
maximum simulation time can be significantly increased. The methods developed
here suggest generalizations that can be applied to simulating interacting
driven-dissipative systems. | [
"Lorenzo Del Re",
"Brian Rost",
"A. F. Kemper",
"J. K. Freericks"
] | [
"IBM"
] | "2019-12-17T23:21:22Z" | 1912.08310v2 |
Performance and error modeling of Deutsch's algorithm in IBM Q | The performance of quantum computers today can be studied by analyzing the
effect of errors in the result of simple quantum algorithms. The modeling and
characterization of these errors is relevant to correct them, for example, with
quantum correcting codes. In this article we characterize the error of the five
qubits quantum computer ibmqx4 (IBM Q), using a Deutsch algorithm and modeling
the error by Generalized Amplitude Damping (GAD) and a unitary misalignment
operation.
Keywords: Quantum Deutsch's algorithm, Quantum error models, IBM Quantum
Experience | [
"Efrain Buksman",
"Andr/'e L. Fonseca de Oliveira",
"Carolina Allende"
] | [
"IBM"
] | "2019-12-16T16:32:22Z" | 1912.07486v1 |
Benchmarking Supercomputers with the Jülich Universal Quantum Computer
Simulator | We use a massively parallel simulator of a universal quantum computer to
benchmark some of the most powerful supercomputers in the world. We find nearly
ideal scaling behavior on the Sunway TaihuLight, the K computer, the IBM
BlueGene/Q JUQUEEN, and the Intel Xeon based clusters JURECA and JUWELS. On the
Sunway TaihuLight and the K computer, universal quantum computers with up to 48
qubits can be simulated by means of an adaptive two-byte encoding to reduce the
memory requirements by a factor of eight. Additionally, we discuss an
alternative approach to alleviate the memory bottleneck by decomposing
entangling gates such that low-depth circuits with a much larger number of
qubits can be simulated. | [
"Dennis Willsch",
"Hannes Lagemann",
"Madita Willsch",
"Fengping Jin",
"Hans De Raedt",
"Kristel Michielsen"
] | [
"IBM"
] | "2019-12-06T17:31:54Z" | 1912.03243v1 |
Evidence of the entanglement constraint on wave-particle duality using
the IBM Q quantum computer | We experimentally verify the link existing between entanglement and the
amount of wave-particle duality in a bipartite quantum system, with
superconducting qubits in the IBM Q quantum computer. We consider both pure and
mixed states, and study the influence of state purity on the observation of the
complementarity "triality" relation of Jakob and Bergou. This work confirms the
quantitative completion of local Bohr's complementarity principle by the
nonlocal quantum entanglement typical of a truly bipartite quantum system. | [
"Nicolas Schwaller",
"Marc-André Dupertuis",
"Clément Javerzac-Galy"
] | [
"IBM"
] | "2019-12-05T16:01:55Z" | 1912.02674v3 |
Towards Efficient Superconducting Quantum Processor Architecture Design | More computational resources (i.e., more physical qubits and qubit
connections) on a superconducting quantum processor not only improve the
performance but also result in more complex chip architecture with lower yield
rate. Optimizing both of them simultaneously is a difficult problem due to
their intrinsic trade-off. Inspired by the application-specific design
principle, this paper proposes an automatic design flow to generate simplified
superconducting quantum processor architecture with negligible performance loss
for different quantum programs. Our architecture-design-oriented profiling
method identifies program components and patterns critical to both the
performance and the yield rate. A follow-up hardware design flow decomposes the
complicated design procedure into three subroutines, each of which focuses on
different hardware components and cooperates with corresponding profiling
results and physical constraints. Experimental results show that our design
methodology could outperform IBM's general-purpose design schemes with better
Pareto-optimal results. | [
"Gushu Li",
"Yufei Ding",
"Yuan Xie"
] | [
"IBM"
] | "2019-11-28T22:15:18Z" | 1911.12879v1 |
Self-testing of quantum states using symmetric local hidden state model | We introduce a symmetric local hidden state $(slhs)$ model in a scenario,
where two spacially separated parties receive quantum states from an unknown
source. We derive an inequality based on the model. A completely new form of
nonlocality emerges from the resource theoretic point of view. The inequality
singles out a larger set of quantum correlated states in the higher dimensional
scenarios $(d> 2 $ X $2)$ than what is predicted by the existing $lhs$ model,
opening a new front for the experimentalists to test the accuracy of the
prediction. We propose an experiment to show the experimental violation of the
inequality in the two qubit scenario and perform the experiment on the IBM
quantum computer. However, the experimental method adopted for the two-qubit
scenario does not naturally generalize in the higher dimensional scenarios and
leaves the experimental verification of the claim open. We also show that the
maximal violation of the inequality can be used to self-test the Bell state and
measurement bases, leading to complete device-independence. | [
"Debasis Mondal",
"Dagomir Kaszlikowski"
] | [
"IBM"
] | "2019-11-18T10:00:24Z" | 1911.07517v3 |
MUQUT: Multi-Constraint Quantum Circuit Mapping on Noisy
Intermediate-Scale Quantum Computers | Rapid advancement in the domain of quantum technologies has opened up
researchers to the real possibility of experimenting with quantum circuits and
simulating small-scale quantum programs. Nevertheless, the quality of currently
available qubits and environmental noise poses a challenge in the smooth
execution of the quantum circuits. Therefore, efficient design automation flows
for mapping a given algorithm to the Noisy Intermediate Scale Quantum (NISQ)
computer becomes of utmost importance. State-of-the-art quantum design
automation tools are primarily focused on reducing logical depth, gate count
and qubit count with the recent emphasis on topology-aware (nearest-neighbor
compliance) mapping. In this work, we extend the technology mapping flows to
simultaneously consider the topology and gate fidelity constraints while
keeping logical depth and gate count as optimization objectives. We provide a
comprehensive problem formulation and multi-tier approach towards solving it.
The proposed automation flow is compatible with commercial quantum computers,
such as IBM QX and Rigetti. Our simulation results over 10 quantum circuit
benchmarks show that the fidelity of the circuit can be improved up to 3.37X
with an average improvement of 1.87X. | [
"Debjyoti Bhattacharjee",
"Abdullah Ash Saki",
"Mahabubul Alam",
"Anupam Chattopadhyay",
"Swaroop Ghosh"
] | [
"IBM",
"Rigetti"
] | "2019-11-16T22:16:53Z" | 1911.08559v1 |
Generalized Boolean Functions and Quantum Circuits on IBM-Q | We explicitly derive a connection between quantum circuits utilising IBM's
quantum gate set and multivariate quadratic polynomials over integers modulo 8.
We demonstrate that the action of a quantum circuit over input qubits can be
written as generalized Walsh-Hadamard transform. Here, we derive the
polynomials corresponding to implementations of the Swap gate and Toffoli gate
using IBM-Q gate set. | [
"Sugata Gangopadhyay",
"Vishvendra Singh Poonia",
"Daattavya Aggarwal",
"Rhea Parekh"
] | [
"IBM"
] | "2019-11-15T19:47:45Z" | 1911.06851v1 |
Experimental Simulation of Hybrid Quantum Systems and Entanglement on a
Quantum Computer | We propose the utilization of the IBM Quantum Experience quantum computing
system to simulate different scenarios involving common hybrid quantum system
components, the Nitrogen Vacancy Centre (NV centre) and the Flux Qubit. We
perform a series of the simulation experiments and demonstrate properties of a
virtual hybrid system, including its spin relaxation rate and state coherence.
In correspondence with experimental investigations we look at the scalability
of such systems and show that increasing the number of coupled NV centres
decreases the coherence time. We also establish the main error rate as a
function of the number of control pulses in evaluating the fidelity of the four
qubit virtual circuit with the simulator. Our results show that the virtual
system can attain decoherence and fidelity values comparable to what has been
reported for experimental investigations of similar physical hybrid systems,
observing a coherence time at 0.35 s for a single NV centre qubit and fidelity
in the range of 0.82. The work thus establishes an effective simulation test
protocol for different technologies to test and analyze them before
experimental investigations or as a supplementary measure. | [
"Farai Mazhandu",
"Kayleigh Mathieson",
"Christopher Coleman",
"Somnath Bhattacharyya"
] | [
"IBM"
] | "2019-11-03T14:28:59Z" | 1911.00897v2 |
A Comparison of Quantum Walk Implementations on NISQ Computers | This paper explores two circuit approaches for quantum walks: the first
consists of generalised controlled inversions, whereas the second one
effectively replaces them with rotation operations around the basis states. We
show the theoretical foundation of the rotational implementation. The
rotational approach nullifies the large amount of ancilla qubits required to
carry out the computation when using the inverter implementation. Our results
concentrate around the comparison of the two architectures in terms of
structure, benefits and detriments, as well as the computational resources
needed for each approach. We show that the inverters approach requires
exponentially fewer gates than the rotations but almost half the number of
qubits in the system. Finally, we execute a number of experiments using an IBM
quantum computer. The experiments show the effects of noise in our circuits.
Small two-qubit quantum walks evolve closer to our expectations, whereas for a
larger number of steps or state space the evolution is severely affected by
noise. | [
"Konstantinos Georgopoulos",
"Clive Emary",
"Paolo Zuliani"
] | [
"IBM"
] | "2019-11-01T11:23:19Z" | 1911.00305v4 |
Optimization of CNOT circuits on limited connectivity architecture | A CNOT circuit is the key gadget for entangling qubits in quantum computing
systems. However, the qubit connectivity of noisy intermediate-scale quantum
(NISQ) devices is constrained by their {limited connectivity architecture}. To
improve the performance of CNOT circuits on NISQ devices, we investigate the
optimization of the size/depth of CNOT circuits under the limited connectivity
architecture. We present a method that can optimize the size of any $n$-qubit
CNOT circuit $O\left(\frac{n^2}{\log \delta}\right)$ on any connected graph
with minimum degree $\delta$, and prove this bound is optimal for the regular
graph. For the near-term sparsely connected structure, we additionally present
a method that can optimize the size of any $n$-qubit CNOT circuit to below
$2n^2$. The numerical experiment shows that our method performs better than
state-of-the-art results. Specifically, we present an example to illustrate the
applicability of our algorithm. For the grid structure, which is commonly used
in current quantum devices, we demonstrate that the depth of any $n$-qubit CNOT
circuit can be optimized to be linear in $n$ with certain ancillary qubits
(ancillas). Experimental results indicate that this method has significant
improvements compared with all of the existing methods. We additionally test
our algorithms on the five-qubit IBMQ devices, and the experiments show that
the measurement results of the optimized circuit with our algorithm are more
robust to noise compared with the IBM mapping method. | [
"Bujiao Wu",
"Xiaoyu He",
"Shuai Yang",
"Lifu Shou",
"Guojing Tian",
"Jialin Zhang",
"Xiaoming Sun"
] | [
"IBM"
] | "2019-10-31T14:13:37Z" | 1910.14478v4 |
Multilevel Combinatorial Optimization Across Quantum Architectures | Emerging quantum processors provide an opportunity to explore new approaches
for solving traditional problems in the post Moore's law supercomputing era.
However, the limited number of qubits makes it infeasible to tackle massive
real-world datasets directly in the near future, leading to new challenges in
utilizing these quantum processors for practical purposes. Hybrid
quantum-classical algorithms that leverage both quantum and classical types of
devices are considered as one of the main strategies to apply quantum computing
to large-scale problems. In this paper, we advocate the use of multilevel
frameworks for combinatorial optimization as a promising general paradigm for
designing hybrid quantum-classical algorithms. In order to demonstrate this
approach, we apply this method to two well-known combinatorial optimization
problems, namely, the Graph Partitioning Problem, and the Community Detection
Problem. We develop hybrid multilevel solvers with quantum local search on
D-Wave's quantum annealer and IBM's gate-model based quantum processor. We
carry out experiments on graphs that are orders of magnitudes larger than the
current quantum hardware size, and we observe results comparable to
state-of-the-art solvers in terms of quality of the solution. | [
"Hayato Ushijima-Mwesigwa",
"Ruslan Shaydulin",
"Christian F. A. Negre",
"Susan M. Mniszewski",
"Yuri Alexeev",
"Ilya Safro"
] | [
"IBM"
] | "2019-10-22T13:56:43Z" | 1910.09985v5 |
Quantum-classical simulation of two-site dynamical mean-field theory on
noisy quantum hardware | We report on a quantum-classical simulation of the single-band Hubbard model
using two-site dynamical mean-field theory (DMFT). Our approach uses IBM's
superconducting qubit chip to compute the zero-temperature impurity Green's
function in the time domain and a classical computer to fit the measured
Green's functions and extract their frequency domain parameters. We find that
the quantum circuit synthesis (Trotter) and hardware errors lead to incorrect
frequency estimates, and subsequently to an inaccurate quasiparticle weight
when calculated from the frequency derivative of the self-energy. These errors
produce incorrect hybridization parameters that prevent the DMFT algorithm from
converging to the correct self-consistent solution. To avoid this pitfall, we
compute the quasiparticle weight by integrating the quasiparticle peaks in the
spectral function. This method is much less sensitive to Trotter errors and
allows the algorithm to converge to self-consistency for a half-filled Mott
insulating system after applying quantum error mitigation techniques to the
quantum simulation data. | [
"Trevor Keen",
"Thomas Maier",
"Steven Johnston",
"Pavel Lougovski"
] | [
"IBM"
] | "2019-10-21T17:05:33Z" | 1910.09512v3 |
Benchmarking quantum computers for real-time evolution of a $(1+1)$
field theory with error mitigation | Quantum computers open the possibility of performing real-time calculations
for quantum field theory scattering processes. We propose to use an index
averaging the absolute value of the difference between the accurately
calculated Trotter evolution of site occupations and their actual measurements
on NISQ machines. The average is over all the qubits for a certain number of
Trotter steps. We use this metric to quantify the progress made in successive
state-of-the-art machines and error-mitigation techniques. We illustrate the
concept with the transverse Ising model in one spatial dimension with four
sites using three of IBM's quantum computers (Almaden, Boeblingen, and
Melbourne). We discuss the size of the Trotter steps needed to achieve physics
goals. Using the proposed metric, we show that readout mitigation methods and
Richardson extrapolations of mitigated measurements are very effective for
specific numbers of Trotter steps of a chosen size. This specific choice can be
applied to other machines and noise mitigation methods. On the other hand, a
reliable algorithmic mitigation would require a significantly larger number of
smaller Trotter steps. | [
"Erik Gustafson",
"Patrick Dreher",
"Zheyue Hang",
"Yannick Meurice"
] | [
"IBM"
] | "2019-10-21T16:10:03Z" | 1910.09478v4 |
Non-unitary operations for ground-state calculations in near term
quantum computers | We introduce a quantum Monte Carlo inspired reweighting scheme to accurately
compute energies from optimally short quantum circuits. This effectively hybrid
quantum-classical approach features both entanglement provided by a short
quantum circuit, and the presence of an effective non-unitary operator at the
same time. The functional form of this projector is borrowed from classical
computation and is able to filter-out high-energy components generated by a
sub-optimal variational quantum heuristic ansatz. The accuracy of this approach
is demonstrated numerically in finding energies of entangled ground-states of
many-body lattice models. We demonstrate a practical implementation on IBM
quantum hardwares up to an 8 qubits circuit. | [
"Guglielmo Mazzola",
"Pauline Ollitrault",
"Panagiotis Barkoutsos",
"Ivano Tavernelli"
] | [
"IBM"
] | "2019-10-04T08:08:01Z" | 1910.01830v1 |
Cloud-Assisted Contracted Simulation of Quantum Chains | The work discusses validation of properties of quantum circuits with many
qubits using non-universal set of quantum gates ensuring possibility of
effective simulation on classical computer. An understanding analogy between
different models of quantum chains is suggested for clarification. An example
with IBM Q Experience cloud platform and Qiskit framework is discussed finally. | [
"Alexander Yu. Vlasov"
] | [
"IBM"
] | "2019-10-03T13:45:17Z" | 1910.01468v2 |
Pairwise tomography networks for many-body quantum systems | We introduce the concept of pairwise tomography networks to characterise
quantum properties in many-body systems and demonstrate an efficient protocol
to measure them experimentally. Pairwise tomography networks are generators of
multiplex networks where each layer represents the graph of a relevant
quantifier such as, e.g., concurrence, quantum discord, purity, quantum mutual
information, or classical correlations. We propose a measurement scheme to
perform two-qubit tomography of all pairs showing exponential improvement in
the number of qubits $N$ with respect to previously existing methods. We
illustrate the usefulness of our approach by means of several examples
revealing its potential impact to quantum computation, communication and
simulation. We perform a proof-of-principle experiment demonstrating pairwise
tomography networks of $W$ states on IBM Q devices. | [
"Guillermo García-Pérez",
"Matteo A. C. Rossi",
"Boris Sokolov",
"Elsi-Mari Borrelli",
"Sabrina Maniscalco"
] | [
"IBM"
] | "2019-09-27T17:35:22Z" | 1909.12814v3 |
Hybrid digital-analog simulation of many-body dynamics with
superconducting qubits | In recent years, there has been a significant progress in the development of
digital quantum processors. The state-of-the-art quantum devices are imperfect,
and fully-algorithmic fault-tolerant quantum computing is a matter of future.
Until technology develops to the state with practical error correction,
computational approaches other than the standard digital one can be used to
avoid execution of the most noisy quantum operations. We demonstrate how a
hybrid digital-analog approach allows simulating dynamics of a transverse-field
Ising model without standard two-qubit gates, which are currently one of the
most problematic building blocks of quantum circuits. We use qubit-qubit
crosstalks (couplings) of IBM superconducting quantum processors to simulate
Trotterized dynamics of spin clusters and then we compare the obtained results
with the results of conventional digital computation based on two-qubit gates
from the universal set. The comparison shows that digital-analog approach
significantly outperforms standard digital approach for this simulation
problem, despite of the fact that crosstalks in IBM quantum processors are
small. We argue that the efficiency of digital-analog quantum computing can be
improved with the help of more specialized processors, so that they can be used
to efficiently implement other quantum algorithms. This indicates the prospect
of a digital-to-analog strategy for near-term noisy intermediate-scale quantum
computers. | [
"D. V. Babukhin",
"A. A. Zhukov",
"W. V. Pogosov"
] | [
"IBM"
] | "2019-09-24T06:51:31Z" | 1909.10732v2 |
Benchmarking Noise Extrapolation with OpenPulse | Distilling precise estimates from noisy intermediate scale quantum (NISQ)
data has recently attracted considerable attention. In order to augment digital
qubit metrics, such as gate fidelity, we discuss analog error mitigability,
i.e. the ability to accurately distill precise observable estimates, as a
hybrid quantum-classical computing benchmarking task. Specifically, we
characterize single qubit error rates on IBM's Poughkeepsie superconducting
quantum hardware, incorporate control-mediated noise dependence into a
generalized rescaling protocol, and analyze how noise characteristics influence
Richardson extrapolation-based error mitigation. Our results identify regions
in the space of Hamiltonian control fields and circuit-depth which are most
amenable to reliable noise extrapolation, as well as shedding light on how
low-level hardware characterization can be used as a predictive tool for
uncertainty quantification in error mitigated NISQ computations. | [
"J. W. O. Garmon",
"R. C. Pooser",
"E. F. Dumitrescu"
] | [
"IBM"
] | "2019-09-11T17:18:31Z" | 1909.05219v1 |
Digital quantum simulation of linear and nonlinear optical elements | We provide a recipe for the digitalization of linear and nonlinear quantum
optics in networks of superconducting qubits. By combining digital techniques
with boson-qubit mappings we address relevant problems which are typically
considered in analog simulators, such as the dynamical Casimir effect or
molecular force fields, including nonlinearities. In this way, the benefits of
digitalization are extended in principle to a new realm of physical problems.
We present preliminary examples launched in IBM Q 5 Tenerife. | [
"Carlos Sabín"
] | [
"IBM"
] | "2019-09-10T11:09:21Z" | 1909.04408v2 |
Quantum classifier with tailored quantum kernel | Kernel methods have a wide spectrum of applications in machine learning.
Recently, a link between quantum computing and kernel theory has been formally
established, opening up opportunities for quantum techniques to enhance various
existing machine learning methods. We present a distance-based quantum
classifier whose kernel is based on the quantum state fidelity between training
and test data. The quantum kernel can be tailored systematically with a quantum
circuit to raise the kernel to an arbitrary power and to assign arbitrary
weights to each training data. Given a specific input state, our protocol
calculates the weighted power sum of fidelities of quantum data in quantum
parallel via a swap-test circuit followed by two single-qubit measurements,
requiring only a constant number of repetitions regardless of the number of
data. We also show that our classifier is equivalent to measuring the
expectation value of a Helstrom operator, from which the well-known optimal
quantum state discrimination can be derived. We demonstrate the
proof-of-principle via classical simulations with a realistic noise model and
experiments using the IBM quantum computer. | [
"Carsten Blank",
"Daniel K. Park",
"June-Koo Kevin Rhee",
"Francesco Petruccione"
] | [
"IBM"
] | "2019-09-05T19:32:37Z" | 1909.02611v2 |
Channel Coding of a Quantum Measurement | In this work, we consider the preservation of a measurement for quantum
systems interacting with an environment. Namely, a method of preserving an
optimal measurement over a channel is devised, what we call channel coding of a
quantum measurement in that operations are applied before and after a channel
in order to protect a measurement. A protocol that preserves a quantum
measurement over an arbitrary channel is shown only with local operations and
classical communication without the use of a larger Hilbert space. Therefore,
the protocol is readily feasible with present day's technologies. Channel
coding of qubit measurements is presented, and it is shown that a measurement
can be preserved for an arbitrary channel for both i) pairs of qubit states and
ii) ensembles of equally probable states. The protocol of preserving a quantum
measurement is demonstrated with IBM quantum computers. | [
"Spiros Kechrimparis",
"Chahan M. Kropf",
"Filip Wudarski",
"Joonwoo Bae"
] | [
"IBM"
] | "2019-08-28T14:09:32Z" | 1908.10735v1 |
Experimental detection of microscopic environments using thermodynamic
observables | Modern thermodynamic theories can be used to study highly complex quantum
dynamics. Here, we experimentally demonstrate that the violation of
thermodynamic constraints allows to detect the coupling of a quantum system to
a hidden environment. By using the IBM quantum superconducting processors, we
perform thermodynamic tests to detect a qubit environment interacting with a
system composed of up to four qubits. The experiments are complemented by
theoretical findings that show efficient scalability of the tests with respect
to system size. Hence, they may be useful to detect an open system dynamics in
situations where other methods (e.g. quantum state tomography) are practically
infeasible. | [
"Ivan Henao",
"Raam Uzdin",
"Nadav Katz"
] | [
"IBM"
] | "2019-08-23T18:26:27Z" | 1908.08968v3 |
Quantum Circuit Transformation Based on Simulated Annealing and
Heuristic Search | Quantum algorithm design usually assumes access to a perfect quantum computer
with ideal properties like full connectivity, noise-freedom and arbitrarily
long coherence time. In Noisy Intermediate-Scale Quantum (NISQ) devices,
however, the number of qubits is highly limited and quantum operation error and
qubit coherence are not negligible. Besides, the connectivity of physical
qubits in a quantum processing unit (QPU) is also strictly constrained.
Thereby, additional operations like SWAP gates have to be inserted to satisfy
this constraint while preserving the functionality of the original circuit.
This process is known as quantum circuit transformation. Adding additional
gates will increase both the size and depth of a quantum circuit and therefore
cause further decay of the performance of a quantum circuit. Thus it is crucial
to minimize the number of added gates. In this paper, we propose an efficient
method to solve this problem. We first choose by using simulated annealing an
initial mapping which fits well with the input circuit and then, with the help
of a heuristic cost function, stepwise apply the best selected SWAP gates until
all quantum gates in the circuit can be executed. Our algorithm runs in time
polynomial in all parameters including the size and the qubit number of the
input circuit, and the qubit number in the QPU. Its space complexity is
quadratic to the number of edges in the QPU. Experimental results on extensive
realistic circuits confirm that the proposed method is efficient and can reduce
by 57% on average the size of the output circuits when compared with the
state-of-the-art algorithm on the most recent IBM quantum device viz. IBM Q20
(Tokyo). | [
"Xiangzhen Zhou",
"Sanjiang Li",
"Yuan Feng"
] | [
"IBM"
] | "2019-08-23T14:54:26Z" | 1908.08853v1 |
An Optimized Quantum Maximum or Minimum Searching Algorithm and its
Circuits | Finding a maximum or minimum is a fundamental building block in many
mathematical models. Compared with classical algorithms, Durr, Hoyer's quantum
algorithm (DHA) achieves quadratic speed. However, its key step, the quantum
exponential searching algorithm (QESA), which is based on Grover algorithm, is
not a sure-success algorithm. Meanwhile, quantum circuits encounter the gate
decomposition problem due to variation of the scale of data. In this paper, we
propose an optimized quantum algorithm for searching maximum and minimum, based
on DHA and the optimal quantum exact search algorithm. Furthermore, we provide
the corresponding quantum circuits, together with three equivalent
simplifications. In circumstances when we can exactly estimate the ratio of the
number of solutions M and the searched space N, our method can improve the
successful probability close to 100%. Furthermore, compared with DHA, our
algorithm shows an advantage in complexity with large databases and in the gate
complexity of constructing oracles. Experiments have been executed on an IBM
superconducting processor with two qubits, and a practical problem of finding
the minimum from Titanic passengers' age was numerically simulated. Both showed
that our optimized maximum or minimum performs more efficiently compared with
DHA. Our algorithm can serve as an important subroutine in various quantum
algorithms which involves searching maximum or minimum. | [
"Yanhu Chen",
"Shijie Wei",
"Xiong Gao",
"Cen Wang",
"Jian Wu",
"Hongxiang Guo"
] | [
"IBM"
] | "2019-08-21T15:47:34Z" | 1908.07943v1 |
SU(2) non-Abelian gauge field theory in one dimension on digital quantum
computers | An improved mapping of one-dimensional SU(2) non-Abelian gauge theory onto
qubit degrees of freedom is presented. This new mapping allows for a reduced
unphysical Hilbert space. Insensitivity to interactions within this unphysical
space is exploited to design more efficient quantum circuits. Local gauge
symmetry is used to analytically incorporate the angular momentum alignment,
leading to qubit registers encoding the total angular momentum on each link.
The results of a multi-plaquette calculation on IBM's quantum hardware are
presented. | [
"Natalie Klco",
"Jesse R. Stryker",
"Martin J. Savage"
] | [
"IBM"
] | "2019-08-19T17:18:26Z" | 1908.06935v1 |
Knapsack Problem variants of QAOA for battery revenue optimisation | We implement two Quantum Approximate Optimisation Algorithm (QAOA) variants
for a battery revenue optimisation problem, equivalent to the weakly NP-hard
Knapsack Problem. Both approaches investigate how to tackle constrained
problems with QAOA. A first 'constrained' approach introduces a quadratic
penalty to enforce the constraint to be respected strictly and reformulates the
problem into an Ising Problem. However, simulations on IBM's simulator
highlight non-convergent results for intermediate depth ($ p\leq 50$). A second
'relaxed' approach applies the QAOA with a non-Ising target function to compute
a linear penalty, running in time $O(p(\log_2 n)^3)$ and needing $O(n \log n)$
qubits. Simulations reveal an exponential improvement over the number of depth
levels and obtain approximations about $0.95$ of the optimum with shallow depth
($p \leq 10$). | [
"Pierre Dupuy de la Grand'rive",
"Jean-Francois Hullo"
] | [
"IBM"
] | "2019-08-06T15:23:34Z" | 1908.02210v2 |
Resource-Efficient Quantum Algorithm for Protein Folding | Predicting the three-dimensional (3D) structure of a protein from its primary
sequence of amino acids is known as the protein folding (PF) problem. Due to
the central role of proteins' 3D structures in chemistry, biology and medicine
applications (e.g., in drug discovery) this subject has been intensively
studied for over half a century. Although classical algorithms provide
practical solutions, sampling the conformation space of small proteins, they
cannot tackle the intrinsic NP-hard complexity of the problem, even reduced to
its simplest Hydrophobic-Polar model. While fault-tolerant quantum computers
are still beyond reach for state-of-the-art quantum technologies, there is
evidence that quantum algorithms can be successfully used on Noisy
Intermediate-Scale Quantum (NISQ) computers to accelerate energy optimization
in frustrated systems. In this work, we present a model Hamiltonian with
$\mathcal{O}(N^4)$ scaling and a corresponding quantum variational algorithm
for the folding of a polymer chain with $N$ monomers on a tetrahedral lattice.
The model reflects many physico-chemical properties of the protein, reducing
the gap between coarse-grained representations and mere lattice models. We use
a robust and versatile optimisation scheme, bringing together variational
quantum algorithms specifically adapted to classical cost functions and
evolutionary strategies (genetic algorithms), to simulate the folding of the 10
amino acid Angiotensin peptide on 22 qubits. The same method is also
successfully applied to the study of the folding of a 7 amino acid neuropeptide
using 9 qubits on an IBM Q 20-qubit quantum computer. Bringing together recent
advances in building gate-based quantum computers with noise-tolerant hybrid
quantum-classical algorithms, this work paves the way towards accessible and
relevant scientific experiments on real quantum processors. | [
"Anton Robert",
"Panagiotis Kl. Barkoutsos",
"Stefan Woerner",
"Ivano Tavernelli"
] | [
"IBM"
] | "2019-08-06T13:49:03Z" | 1908.02163v1 |
Subsets and Splits