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  • Qubit coupled cluster singles and doubles variational quantum eigensolver ansatz for electronic structure calculations
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-10-20
    Rongxin Xia and Sabre Kais

    Variational quantum eigensolver (VQE) for electronic structure calculations is believed to be one major potential application of near term quantum computing. Among all proposed VQE algorithms, the unitary coupled cluster singles and doubles excitations (UCCSD) VQE ansatz has achieved high accuracy and received a lot of research interest. However, the UCCSD VQE based on fermionic excitations needs extra

  • Quantum-feedback-controlled macroscopic quantum nonlocality in cavity optomechanics
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-10-19
    Yaqin Luo and Huatang Tan

    In this paper, we propose a continuous measurement and feedback scheme to achieve strong Einstein–Podolsky–Rosen (EPR) steering and Bell nonlocality of two macroscopic mechanical oscillators in cavity optomechanics. Our system consists of two optomechanical cavities in which two cavity fields are coupled to each other via nondegenerate parametric downconversion. The two cavity output fields are subject

  • Polyatomic molecules as quantum sensors for fundamental physics
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-10-16
    Nicholas R Hutzler

    Precision measurements in molecules have advanced rapidly in recent years through developments in techniques to cool, trap, and control. The complexity of molecules makes them a challenge to study, but also offers opportunities for enhanced sensitivity to many interesting effects. Polyatomic molecules offer additional complexity compared to diatomic molecules, yet are still ‘simple’ enough to be laser-cooled

  • Quantum implementation of an artificial feed-forward neural network
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-10-14
    Francesco Tacchino, Panagiotis Barkoutsos, Chiara Macchiavello, Ivano Tavernelli, Dario Gerace and Daniele Bajoni

    Artificial intelligence algorithms largely build on multi-layered neural networks. Coping with their increasing complexity and memory requirements calls for a paradigmatic change in the way these powerful algorithms are run. Quantum computing promises to solve certain tasks much more efficiently than any classical computing machine, and actual quantum processors are now becoming available through cloud

  • To quantum or not to quantum: towards algorithm selection in near-term quantum optimization
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-10-13
    Charles Moussa, Henri Calandra and Vedran Dunjko

    The Quantum approximate optimization algorithm (QAOA) constitutes one of the often mentioned candidates expected to yield a quantum boost in the era of near-term quantum computing. In practice, quantum optimization will have to compete with cheaper classical heuristic methods, which have the advantage of decades of empirical domain-specific enhancements. Consequently, to achieve optimal performance

  • Using models to improve optimizers for variational quantum algorithms
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-10-05
    Kevin J Sung, Jiahao Yao, Matthew P Harrigan, Nicholas C Rubin, Zhang Jiang, Lin Lin, Ryan Babbush and Jarrod R McClean

    Variational quantum algorithms are a leading candidate for early applications on noisy intermediate-scale quantum computers. These algorithms depend on a classical optimization outer-loop that minimizes some function of a parameterized quantum circuit. In practice, finite sampling error and gate errors make this a stochastic optimization with unique challenges that must be addressed at the level of

  • The bitter truth about gate-based quantum algorithms in the NISQ era
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-24
    Frank Leymann and Johanna Barzen

    Implementing a gate-based quantum algorithm on an noisy intermediate scale quantum (NISQ) device has several challenges that arise from the fact that such devices are noisy and have limited quantum resources. Thus, various factors contributing to the depth and width as well as to the noise of an implementation of a gate-based algorithm must be understood in order to assess whether an implementation

  • Speedup of Grover’s search algorithm and closed timelike curves
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-22
    Ki Hyuk Yee, Jeongho Bang, Paul M Alsing, Warner A Miller and Doyeol Ahn

    The quadratic reduction of query complexity of Grover’s search algorithm (GA), while significant, would not be enough to enjoy exponentially fast data searching in large-scale quantum computation. One of the ways to enhance the speedup in the framework of Grover’s algorithm is to employ a novel quantum operation, i.e., inversion against an unknown state; however, this is not possible at least in quantum

  • Fault-tolerance thresholds for code conversion schemes with quantum Reed–Muller codes
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-17
    Lan Luo, Zhi Ma, Dongdai Lin and Hong Wang

    Code concatenation and conversion are two prominent methods to realize universal fault-tolerant quantum computation without the need for magic state distillation. In this paper, we analyze three quantum Reed–Muller (QRM) codes of different code lengths under code conversion schemes, and compare them with the 105-qubit concatenated code on optimized encoding circuits. The depolarizing error thresholds

  • Spatial entanglement and state engineering via four-photon Hong–Ou–Mandel interference
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-17
    A Ferreri, V Ansari, B Brecht, C Silberhorn and P R Sharapova

    The phenomenon of entanglement is the basis of quantum information and quantum communication processes. Entangled systems with a large number of photons are of great interest at present because they provide a platform for streaming technologies based on photonics. In this paper we present a device which operates with four-photons and based on the Hong–Ou–Mandel interference. The presented device allows

  • Simulating integrated photonic gates using FDTD
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-17
    Andrei-Emanuel Dragomir, Cristian George Ivan and Radu Ionicioiu

    Quantum technologies, such as quantum communication, quantum sensing, quantum imaging and quantum computation, need a platform which is flexible, miniaturisable and works at room temperature. Integrated photonics is a promising and fast-developing platform. This requires to develop the right tools to design and fabricate arbitrary photonic quantum devices. Here we present an algorithm which, starting

  • Active controlled dual-band unidirectional reflectionlessness by classical driving field in non-Hermitian quantum system
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-17
    Hang Yang, De Xiu Qiu, Xin Yu Zou, Chengshou An, Ying Qiao Zhang and Xing Ri Jin

    We propose a scheme to realize the active controlled dual-band unidirectional reflectionlessness at exceptional points by classical driving field in a non-Hermitian quantum system that consists of two Λ-type three-level quantum dots side coupled to a plasmonic waveguide. We demonstrate that the dual-band unidirectional reflectionlessness can be controlled by appropriately tuning classical driving field

  • Upper bounds for relative entropy of entanglement based on active learning
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-17
    Shi-Yao Hou, Chenfeng Cao, D L Zhou and Bei Zeng

    Quantifying entanglement for multipartite quantum state is a crucial task in many aspects of quantum information theory. Among all the entanglement measures, relative entropy of entanglement E R is an outstanding quantity due to its clear geometric meaning, easy compatibility with different system sizes, and various applications in many other related quantity calculations. Lower bounds of E R were

  • Witnessing non-objectivity in the framework of strong quantum Darwinism
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-13
    Thao P Le and Alexandra Olaya-Castro

    Quantum Darwinism is a compelling theory that describes the quantum-to classical transition as the emergence of objectivity of quantum systems. Spectrum broadcast structure and strong quantum Darwinism are two extensions of this theory with emphasis on state structure and information respectively. The complete experimental verification of these three frameworks, however, requires quantum state tomography

  • Protocols for long-distance quantum communication with single 167 Er ions
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-07
    F Kimiaee Asadi, S C Wein and C Simon

    We design a quantum repeater architecture using individual 167 Er ions doped into Y 2 SiO 5 crystal. This ion is a promising candidate for a repeater protocol because of its long hyperfine coherence time in addition to its ability to emit photons within the telecommunication wavelength range. To distribute entanglement over a long distance, we propose two different swapping gates between nearby ions

  • How to transform graph states using single-qubit operations: computational complexity and algorithms
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-07
    Axel Dahlberg, Jonas Helsen and Stephanie Wehner

    Graph states are ubiquitous in quantum information with diverse applications ranging from quantum network protocols to measurement based quantum computing. Here we consider the question whether one graph ( source ) state can be transformed into another graph ( target ) state, using a specific set of quantum operations (LC + LPM + CC): single-qubit Clifford operations (LC), single-qubit Pauli measurements

  • Adiabatic preparation of entangled, magnetically ordered states with cold bosons in optical lattices
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-07
    Araceli Venegas-Gomez, Johannes Schachenmayer, Anton S Buyskikh, Wolfgang Ketterle, Maria Luisa Chiofalo and Andrew J Daley

    We analyze a scheme for preparation of magnetically ordered states of two-component bosonic atoms in optical lattices. We compute the dynamics during adiabatic and optimized time-dependent ramps to produce ground states of effective spin Hamiltonians, and determine the robustness to decoherence for realistic experimental system sizes and timescales. Ramping parameters near a phase transition point

  • Enhanced repulsively bound atom pairs in topological optical lattice ladders
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-07
    Stuart Flannigan and Andrew J Daley

    There is a growing interest in using cold-atom systems to explore the effects of strong interactions in topological band structures. Here we investigate interacting bosons in a Cruetz ladder, which is characterised by topological flat energy bands where it has been proposed that interactions can lead to the formation of bound atomic pairs giving rise to pair superfluidity. By investigating realistic

  • Quantum speedups of some general-purpose numerical optimisation algorithms
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-09-07
    Cezar-Mihail Alexandru, Ella Bridgett-Tomkinson, Noah Linden, Joseph MacManus, Ashley Montanaro and Hannah Morris

    We give quantum speedups of several general-purpose numerical optimisation methods for minimising a function ##IMG## [http://ej.iop.org/images/2058-9565/5/4/045014/qstabb003ieqn1.gif] {$f:{\mathbb{R}}^{n}\to \mathbb{R}$} . First, we show that many techniques for global optimisation under a Lipschitz constraint can be accelerated near-quadratically. Second, we show that backtracking line search, an

  • Qiskit pulse: programming quantum computers through the cloud with pulses
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-08-24
    Thomas Alexander, Naoki Kanazawa, Daniel J Egger, Lauren Capelluto, Christopher J Wood, Ali Javadi-Abhari and David C McKay

    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 [1]. To demonstrate

  • Optimizing quantum phase estimation for the simulation of Hamiltonian eigenstates
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-08-17
    P M Q Cruz, G Catarina, R Gautier and J Fernández-Rossier

    We revisit quantum phase estimation algorithms for the purpose of obtaining the energy levels of many-body Hamiltonians and pay particular attention to the statistical analysis of their outputs. We introduce the mean phase direction of the parent distribution associated with eigenstate inputs as a new post-processing tool. By connecting it with the unknown phase, we find that if used as its direct

  • Limitations of error corrected quantum annealing in improving the performance of Boltzmann machines
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-08-17
    Richard Y Li, Tameem Albash and Daniel A Lidar

    Boltzmann machines, a class of machine learning models, are the basis of several deep learning methods that have been successfully applied to both supervised and unsupervised machine learning tasks. These models assume that some given dataset is generated according to a Boltzmann distribution, and the goal of the training procedure is to learn the set of parameters that most closely match the input

  • Quantum algorithm for hyperparameters estimation
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-08-16
    Rui Huang, Xiaoqing Tan and Qingshan Xu

    Hyperparameters play an important role in machine learning algorithms, such as linear regression and support vector machines. In this paper, we present a quantum hyperparameters estimation (QHE) algorithm and design the corresponding quantum circuit to accomplish HE effectively. Then we analyze the complexity, probability, and fidelity of the whole algorithm. Finally, we deploy a numerical simulation

  • Self-calibrating optical low-coherence reflectometry with energy-time entangled photons for absolute distance measurements
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-08-16
    Manuel Unternährer and André Stefanov

    Optical low-coherence reflectometry is capable of unambiguously measuring positions of stacked, partially reflective layers in a sample object. It relies on the low coherence of the light source and the absolute distances are obtained from the position reading of a mechanical motor stage. We show how to exploit the simultaneous high and low coherence properties of energy-time entangled photon pairs

  • Benchmarking near-term devices with quantum error correction
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-08-02
    James R Wootton

    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 topological_codes module of Qiskit-Ignis, which is designed to provide the tools necessary to perform such tests. Specifically

  • Constant depth fault-tolerant Clifford circuits for multi-qubit large block codes
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-29
    Yi-Cong Zheng, Ching-Yi Lai, Todd A Brun and Leong-Chuan Kwek

    Fault-tolerant quantum computation (FTQC) schemes using large block codes that encode k > 1 qubits in n physical qubits can potentially reduce the resource overhead to a great extent because of their high encoding rate. However, the fault-tolerant (FT) logical operations for the encoded qubits are difficult to find and implement, which usually takes not only a very large resource overhead but also

  • Experimental control of the degree of non-classicality via quantum coherence
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-22
    A Smirne, T Nitsche, D Egloff, S Barkhofen, S De, I Dhand, C Silberhorn, S F Huelga and M B Plenio

    The origin of non-classicality in physical systems and its connection to distinctly quantum features such as entanglement and coherence is a central question in quantum physics. This work analyses this question theoretically and experimentally, linking quantitatively non-classicality with quantum coherence. On the theoretical front, we show when the coherence of an observable is linearly related to

  • Finding semi-optimal measurements for entanglement detection using autoencoder neural networks
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-20
    Mohammad Yosefpor, Mohammad Reza Mostaan and Sadegh Raeisi

    Entanglement is one of the key resources of quantum information science which makes identification of entangled states essential to a wide range of quantum technologies and phenomena. This problem is however both computationally and experimentally challenging. Here we use autoencoder neural networks to find semi-optimal set of incomplete measurements that are most informative for the detection of entangled

  • A quantum deep convolutional neural network for image recognition
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-19
    YaoChong Li, Ri-Gui Zhou, RuQing Xu, Jia Luo and WenWen Hu

    Deep learning achieves unprecedented success involves many fields, whereas the high requirement of memory and time efficiency tolerance have been the intractable challenges for a long time. On the other hand, quantum computing shows its superiorities in some computation problems owing to its intrinsic properties of superposition and entanglement, which may provide a new path to settle these issues

  • OAM tomography with Heisenberg–Weyl observables
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-13
    Alexandra Maria Pălici, Tudor-Alexandru Isdrailă, Stefan Ataman and Radu Ionicioiu

    Photons carrying orbital angular momentum (OAM) are excellent qudits and are widely used in several applications, such as long distance quantum communication, d -dimensional teleportation and high-resolution imaging and metrology. All these protocols rely on quantum tomography to characterise the OAM state, which currently requires complex measurements involving spatial light modulators and mode filters

  • Validating multi-photon quantum interference with finite data
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-13
    Fulvio Flamini, Mattia Walschaers, Nicolò Spagnolo, Nathan Wiebe, Andreas Buchleitner and Fabio Sciarrino

    Multi-particle interference is a key resource for quantum information processing, as exemplified by Boson Sampling. Hence, given its fragile nature, an essential desideratum is a solid and reliable framework for its validation. However, while several protocols have been introduced to this end, the approach is still fragmented and fails to build a big picture for future developments. In this work, we

  • Corrigendum: Long-lived state in a four-spin system hyperpolarized at room temperature
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-08
    Koichiro Miyanishi, Naoki Ichijo, Makoto Motoyama, Akinori Kagawa, Makoto Negoro and Masahiro Kitagawa

    Description unavailable

  • Probing quantum processor performance with pyGSTi
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-08
    Erik Nielsen, Kenneth Rudinger, Timothy Proctor, Antonio Russo, Kevin Young and Robin Blume-Kohout

    PyGSTi is a Python software package for assessing and characterizing the performance of quantum computing processors. It can be used as a standalone application, or as a library, to perform a wide variety of quantum characterization, verification, and validation (QCVV) protocols on as-built quantum processors. We outline pyGSTi’s structure, and what it can do, using multiple examples. We cover its

  • Towards scalable bosonic quantum error correction
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-08
    B M Terhal, J Conrad and C Vuillot

    We review some of the recent efforts in devising and engineering bosonic qubits for superconducting devices, with emphasis on the Gottesman–Kitaev–Preskill (GKP) qubit. We present some new results on decoding repeated GKP error correction using finitely-squeezed GKP ancilla qubits, exhibiting differences with previously studied stochastic error models. We discuss circuit-QED ways to realize CZ gates

  • An open-source, industrial-strength optimizing compiler for quantum programs
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-07-06
    R S Smith, E C Peterson, M G Skilbeck and E J Davis

    Quilc is an open-source, optimizing compiler for gate-based quantum programs written in Quil or QASM, two popular quantum programming languages. The compiler was designed with attention toward NISQ-era quantum computers, specifically recognizing that each quantum gate has a non-negligible and often irrecoverable cost toward a program’s successful execution. Quilc ’s primary goal is to make authoring

  • Phase-tunable quantum router
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-29
    Guo-An Yan, Wen-Qing Cheng and Hua Lu

    We propose and analyze an efficient scheme for realizing the high transfer rate for quantum router composed of two coupled-resonator waveguides (CRWs) channels coupled with N sequential cavities with embedded N four-level atoms. In this paper, we focus on the effect of the phase difference between different coupling constants which has been ignored in the previous works. In this scheme, we demonstrate

  • Noisy distributed sensing in the Bayesian regime
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-29
    S Wölk, P Sekatski and W Dür

    We consider non-local sensing of scalar signals with specific spatial dependence in the Bayesian regime. We design schemes that allow one to achieve optimal scaling and are immune to noise sources with a different spatial dependence than the signal. This is achieved by using a sensor array of spatially separated sensors and constructing a multi-dimensional decoherence free subspace. While in the Fisher

  • Generating microwave photon Fock states in a circuit QED via invariant-based shortcuts to adiabaticity
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-29
    Run-Ying Yan and Zhi-Bo Feng

    Optimal generation of photon Fock states is of significance to quantum science and technology. Here we develop a theoretical scheme for fast generating microwave photon Fock states in a circuit quantum electrodynamics (QED) via invariant-based shortcuts to adiabaticity. A superconducting transmon qubit is dispersively coupled to a cavity field of transmission line resonator. Two classical drivings

  • staq —A full-stack quantum processing toolkit
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-25
    Matthew Amy and Vlad Gheorghiu

    We describe staq , a full-stack quantum processing toolkit written in standard C++. staq is a quantum compiler toolkit, comprising of tools that range from quantum optimizers and translators to physical mappers for quantum devices with restricted connectives. The design of staq is inspired from the UNIX philosophy of ‘less is more’, i.e. staq achieves complex functionality via combining (piping) small

  • Corrigendum: Randomized benchmarking in the analogue setting (2020 Quantum Sci. Technol. 5 034001 [http://doi.org/10.1088/2058-9565/ab7eec] )
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-23
    E Derbyshire, J Yago Malo, A J Daley, E Kashefi and P Wallden

    Description unavailable

  • Thermodynamics of a quantum annealer
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-17
    Lorenzo Buffoni and Michele Campisi

    The D-wave processor is a partially controllable open quantum system that exchanges energy with its surrounding environment (in the form of heat) and with the external time dependent control fields (in the form of work). Despite being rarely thought as such, it is a thermodynamic machine. Here we investigate the properties of the D-Wave quantum annealers from a thermodynamical perspective. We performed

  • Minimum hardware requirements for hybrid quantum–classical DMFT
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-17
    B Jaderberg, A Agarwal, K Leonhardt, M Kiffner and D Jaksch

    We numerically emulate noisy intermediate-scale quantum (NISQ) devices and determine the minimal hardware requirements for two-site hybrid quantum–classical dynamical mean-field theory (DMFT). We develop a circuit recompilation algorithm which significantly reduces the number of quantum gates of the DMFT algorithm and find that the quantum–classical algorithm converges if the two-qubit gate fidelities

  • Entanglement of truncated quantum states
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-17
    Giacomo Sorelli, Vyacheslav N Shatokhin, Filippus S Roux and Andreas Buchleitner

    We investigate the impact of Hilbert-space truncation upon the entanglement of an initially maximally entangled m × m bipartite quantum state, after propagation under an entanglement-preserving n × n ( n ⩾ m ) unitary. Truncation—physically enforced, e.g., by a detector’s finite cross section—projects the state onto an s × s -dimensional subspace (3 ⩽ s ⩽ n ). For a random local unitary evolution,

  • OpenFermion: the electronic structure package for quantum computers
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-14
    JarrodR McClean, Nicholas C Rubin, Kevin J Sung, Ian D Kivlichan, Xavier Bonet-Monroig, Yudong Cao, Chengyu Dai, E Schuyler Fried, Craig Gidney, Brendan Gimby, Pranav Gokhale, Thomas Häner, Tarini Hardikar, Vojtěch Havlíček, Oscar Higgott, Cupjin Huang, Josh Izaac, Zhang Jiang, Xinle Liu, Sam McArdle, Matthew Neeley, Thomas O’Brien, Bryan O’Gorman, Isil Ozfidan, Maxwell D Radin, Jhonathan Romero, Nicolas

    Quantum simulation of chemistry and materials is predicted to be an important application for both near-term and fault-tolerant quantum devices. However, at present, developing and studying algorithms for these problems can be difficult due to the prohibitive amount of domain knowledge required in both the area of chemistry and quantum algorithms. To help bridge this gap and open the field to more

  • Rigorous measurement error correction
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-08
    Michael R Geller

    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 Γ acting on the output probability

  • Quantum computation of an interacting fermionic model
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-07
    Chinmay Mishra, Shane Thompson, Raphael Pooser and George Siopsis

    Relativistic fermionic field theories constitute the fundamental description of all observable matter. The simplest of the models provide a useful, classically verifiable benchmark for noisy intermediate scale quantum computers. We calculate the energy levels of a model of Dirac fermions with four-fermion interactions, on a lattice in 1 + 1 space-time dimensions. We employ a hybrid classical-quantum

  • Two-body quantum absorption refrigerators with optomechanical-like interactions
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-03
    M Tahir Naseem, Avijit Misra and Özgür E Müstecaplıoğlu

    Quantum absorption refrigerator (QAR) autonomously extracts heat from a cold bath and dumps into a hot bath by exploiting the input heat from a higher temperature reservoir. QARs typically require three-body interactions. We propose and examine a two-body QAR model based upon optomechanical-like coupling in the working medium composed of either two two-level systems or two harmonic oscillators or one

  • Inhomogeneous driving in quantum annealers can result in orders-of-magnitude improvements in performance
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-03
    Juan I Adame and Peter L McMahon

    Quantum annealers are special-purpose quantum computers that primarily target solving Ising optimization problems. Theoretical work has predicted that the probability of a quantum annealer ending in a ground state can be dramatically improved if the spin driving terms, which play a crucial role in the functioning of a quantum annealer, have different strengths for different spins; that is, they are

  • Efficient microwave frequency conversion mediated by a photonics compatible silicon nitride nanobeam oscillator
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-06-01
    J M Fink, M Kalaee, R Norte, A Pitanti and O Painter

    Microelectromechanical systems and integrated photonics provide the basis for many reliable and compact circuit elements in modern communication systems. Electro-opto-mechanical devices are currently one of the leading approaches to realize ultra-sensitive, low-loss transducers for an emerging quantum information technology. Here we present an on-chip microwave frequency converter based on a planar

  • Lower bounds on the non-Clifford resources for quantum computations
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-31
    Michael Beverland, Earl Campbell, Mark Howard and Vadym Kliuchnikov

    Treating stabilizer operations as free, we establish lower bounds on the number of resource states, also known as magic states, needed to perform various quantum computing tasks. Our bounds apply to adaptive computations using measurements with an arbitrary number of stabilizer ancillas. We consider (1) resource state conversion, (2) single-qubit unitary synthesis, and (3) computational subroutines

  • Certification of a functionality in a quantum network stage
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-31
    Victoria Lipinska, Lê Phuc Thinh, Jérémy Ribeiro and Stephanie Wehner

    We consider testing the ability of quantum network nodes to execute multi-round quantum protocols. Specifically, we examine protocols in which the nodes are capable of performing quantum gates, storing qubits and exchanging said qubits over the network a certain number of times. We propose a simple ping-pong test, which provides a certificate for the capability of the nodes to run certain multi-round

  • Witnessing entanglement in experiments with correlated noise
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-31
    Bas Dirkse, Matteo Pompili, Ronald Hanson, Michael Walter and Stephanie Wehner

    The purpose of an entanglement witness experiment is to certify the creation of an entangled state from a finite number of trials. The statistical confidence of such an experiment is typically expressed as the number of observed standard deviations of witness violations. This method implicitly assumes that the noise is well-behaved so that the central limit theorem applies. In this work, we propose

  • An updated LLVM-based quantum research compiler with further OpenQASM support
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-27
    Andrew Litteken, Yung-Ching Fan, Devina Singh, Margaret Martonosi and Frederic T Chong

    Quantum computing is a rapidly growing field with the potential to change how we solve previously intractable problems. Emerging hardware is approaching a complexity that requires increasingly sophisticated programming and control. Scaffold is an older quantum programming language that was originally designed for resource estimation for far-future, large quantum machines, and ScaffCC is the corresponding

  • QuESTlink—Mathematica embiggened by a hardware-optimised quantum emulator
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-27
    Tyson Jones and Simon Benjamin

    We introduce QuESTlink,pronounced ‘quest link’, an open-source Mathematicapackage which efficiently emulates quantum computers. By integratingwith the Quantum Exact Simulation Toolkit (QuEST), QuESTlink offers ahigh-level, expressive and usable interface to a high-performance, hardware-accelerated emulator. Requiring no installation, QuESTlink streamlines the powerful analysis capabilities of Mathematica

  • Quantum scrambling and the growth of mutual information
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-25
    Akram Touil and Sebastian Deffner

    Quantum information scrambling refers to the loss of local recoverability of quantum information, which has found widespread attention from high energy physics to quantum computing. In the present analysis we propose a possible starting point for the development of a comprehensive framework for the thermodynamics of scrambling. To this end, we prove that the growth of entanglement as quantified by

  • Applications of near-term photonic quantum computers: software and algorithms
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-20
    Thomas R Bromley, Juan Miguel Arrazola, Soran Jahangiri, Josh Izaac, Nicolás Quesada, Alain Delgado Gran, Maria Schuld, Jeremy Swinarton, Zeid Zabaneh and Nathan Killoran

    Gaussian boson sampling (GBS) is a near-term platform for photonic quantum computing. Recent efforts have led to the discovery of GBS algorithms with applications to graph-based problems, point processes, and molecular vibronic spectra in chemistry. The development of dedicated quantum software is a key enabler in permitting users to program devices and implement algorithms. In this work, we introduce

  • Figures of merit for quantum transducers
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-18
    Emil Zeuthen, Albert Schliesser, Anders S Sørensen and Jacob M Taylor

    Recent technical advances have sparked renewed interest in physical systems that couple simultaneously to different parts of the electromagnetic spectrum, thus enabling transduction of signals between vastly different frequencies at the level of single quanta. Such hybrid systems have demonstrated frequency conversion of classical signals and have the potential of enabling quantum state transfer, e

  • Training the quantum approximate optimization algorithm without access to a quantum processing unit
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-11
    Michael Streif and Martin Leib

    In this paper, we eliminate the classical outer learning loop of the quantum approximate optimization algorithm (QAOA) and present a strategy to find good parameters for QAOA based on topological arguments of the problem graph and tensor network techniques. Starting from the observation of the concentration of control parameters of QAOA, we find a way to classically infer parameters which scales polynomially

  • A quantum algorithm to efficiently sample from interfering binary trees
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-10
    Davide Provasoli, Benjamin Nachman, Christian Bauer and Wibe A de Jong

    Quantum computers provide an opportunity to efficiently sample from probability distributions that include non-trivial interference effects between amplitudes. Using a simple process wherein all possible state histories can be specified by a binary tree, we construct an explicit quantum algorithm for an important three-dimensional subspace of the parameter space that runs in polynomial time to sample

  • Quantum electronics and optics at the interface of solid neon and superfluid helium
    Quantum Sci. Technol. (IF 4.041) Pub Date : 2020-05-10
    Dafei Jin

    We predict a new quantum electronic structure at the interface between two condensed phases of noble-gas elements: solid neon and superfluid helium. An excess electron injected onto this interface self-confines its wavefunction into a nanometric dome structure. Its size varies with pressure and optical transitions cover a broad mid-infrared spectrum. A collection of such electrons can form a classical

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