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PRA: Quantum information

Recently published articles in Phys. Rev. A in the Table of Content section "Quantum information"

Published: 2017-10-19T05:02:23+00:00


Optimal convex approximations of quantum states


Author(s): Massimiliano F. Sacchi

We consider the problem of optimally approximating an unavailable quantum state $ρ$ by the convex mixing of states drawn from a set of available states ${{ν}_{i}}$. The problem is recast to look for the least distinguishable state from $ρ$ among the convex set ${∑}_{i}{p}_{i}{ν}_{i}$, and the corres...

[Phys. Rev. A 96, 042325] Published Wed Oct 18, 2017

Investigating Einstein-Podolsky-Rosen steering of continuous-variable bipartite states by non-Gaussian pseudospin measurements


Author(s): Yu Xiang, Buqing Xu, Ladislav Mišta, Jr., Tommaso Tufarelli, Qiongyi He, and Gerardo Adesso

Einstein-Podolsky-Rosen (EPR) steering is an asymmetric form of correlations which is intermediate between quantum entanglement and Bell nonlocality, and can be exploited as a resource for quantum communication with one untrusted party. In particular, steering of continuous-variable Gaussian states ...

[Phys. Rev. A 96, 042326] Published Wed Oct 18, 2017

Entanglement-enhanced lidars for simultaneous range and velocity measurements


Author(s): Quntao Zhuang, Zheshen Zhang, and Jeffrey H. Shapiro

Lidar is a well-known optical technology for measuring a target's range and radial velocity. We describe two lidar systems that use entanglement between transmitted signals and retained idlers to obtain significant quantum enhancements in simultaneous measurements of these parameters. The first enta...

[Phys. Rev. A 96, 040304(R)] Published Mon Oct 16, 2017

Transfer and preservation of entanglement in a hybrid optomechanical system


Author(s): Qiankun Zhang, Xiangyang Zhang, and Lianzhen Liu

We propose a scheme for entangling a movable mirror and two atomic ensembles in a coupled hybrid optomechanical system. Using the logarithmic negativity for the entanglement measure, we analyze the effect of the coupling strength between the two cavities on the entanglement of the movable mirror and...

[Phys. Rev. A 96, 042320] Published Mon Oct 16, 2017

Verifying bound entanglement of dephased Werner states


Author(s): P. Thomas, M. Bohmann, and W. Vogel

The verification of quantum entanglement under the influence of realistic noise and decoherence is crucial for the development of quantum technologies. Unfortunately, a full entanglement characterization is generally not possible with most entanglement criteria such as entanglement witnesses or the ...

[Phys. Rev. A 96, 042321] Published Mon Oct 16, 2017

Experimental demonstration of perturbative anticrossing mitigation using nonuniform driver Hamiltonians


Author(s): Trevor Lanting, Andrew D. King, Bram Evert, and Emile Hoskinson

Perturbative anticrossings have long been identified as a potential computational bottleneck for quantum annealing. This bottleneck can appear, for example, when a uniform transverse driver Hamiltonian is applied to each qubit. Previous theoretical research sought to alleviate such anticrossings by ...

[Phys. Rev. A 96, 042322] Published Mon Oct 16, 2017

Tight upper bound for the maximal quantum value of the Svetlichny operators


Author(s): Ming Li, Shuqian Shen, Naihuan Jing, Shao-Ming Fei, and Xianqing Li-Jost

It is a challenging task to detect genuine multipartite nonlocality (GMNL). In this paper, the problem is considered via computing the maximal quantum value of Svetlichny operators for three-qubit systems and a tight upper bound is obtained. The constraints on the quantum states for the tightness of...

[Phys. Rev. A 96, 042323] Published Mon Oct 16, 2017

Role of coherence during classical and quantum decoherence


Author(s): Jin-Xing Hou, Si-Yuan Liu, Xiao-Hui Wang, and Wen-Li Yang

The total correlation in a bipartite quantum system is measured by the quantum mutual information $\mathcal{I}$, which consists of quantum discord and classical correlation. However, recent results in quantum information show that coherence, which is a part of total correlation, is more general and ...

[Phys. Rev. A 96, 042324] Published Mon Oct 16, 2017

Thermal effects on coherence and excitation transfer


Author(s): Laleh Memarzadeh and Azam Mani

To control and utilize quantum features in small scale for practical applications such as quantum transport, it is crucial to gain a deep understanding of the quantum characteristics of states such as coherence. Here by introducing a technique that simplifies solving the dynamical equation, we study...

[Phys. Rev. A 96, 042318] Published Fri Oct 13, 2017

Estimation of gradients in quantum metrology


Author(s): Sanah Altenburg, Michał Oszmaniec, Sabine Wölk, and Otfried Gühne

We develop a general theory to estimate magnetic field gradients in quantum metrology. We consider a system of $N$ particles distributed on a line whose internal degrees of freedom interact with a magnetic field. Usually gradient estimation is based on precise measurements of the magnetic field at t...

[Phys. Rev. A 96, 042319] Published Fri Oct 13, 2017

Resonator reset in circuit QED by optimal control for large open quantum systems


Author(s): Samuel Boutin, Christian Kraglund Andersen, Jayameenakshi Venkatraman, Andrew J. Ferris, and Alexandre Blais

We study an implementation of the open GRAPE (gradient ascent pulse engineering) algorithm well suited for large open quantum systems. While typical implementations of optimal control algorithms for open quantum systems rely on explicit matrix exponential calculations, our implementation avoids thes...

[Phys. Rev. A 96, 042315] Published Thu Oct 12, 2017

Fault-tolerance thresholds for the surface code with fabrication errors


Author(s): James M. Auger, Hussain Anwar, Mercedes Gimeno-Segovia, Thomas M. Stace, and Dan E. Browne

The construction of topological error correction codes requires the ability to fabricate a lattice of physical qubits embedded on a manifold with a nontrivial topology such that the quantum information is encoded in the global degrees of freedom (i.e., the topology) of the manifold. However, the man...

[Phys. Rev. A 96, 042316] Published Thu Oct 12, 2017

Quantum gate description for induced coherence without induced emission and its applications


Author(s): Sahar Alipour, Mario Krenn, and Anton Zeilinger

We introduce unitary quantum gates for photon pair creation in spontaneous parametric down-conversion nonlinear crystals (NLs) and for photon path alignment. These are the two key ingredients for the method of induced coherence without induced emission and many ensuing variations thereof. The diffic...

[Phys. Rev. A 96, 042317] Published Thu Oct 12, 2017

Optimally cloned binary coherent states


Author(s): C. R. Müller, G. Leuchs, Ch. Marquardt, and U. L. Andersen

Binary coherent state alphabets can be represented in a two-dimensional Hilbert space. We capitalize this formal connection between the otherwise distinct domains of qubits and continuous variable states to map binary phase-shift keyed coherent states onto the Bloch sphere and to derive their quantu...

[Phys. Rev. A 96, 042311] Published Wed Oct 11, 2017

Imperfect state preparation in continuous-variable quantum key distribution


Author(s): Wenyuan Liu, Xuyang Wang, Ning Wang, Shanna Du, and Yongmin Li

In continuous-variable quantum key distribution, the loss and excess noise of the quantum channel are key parameters that determine the secure key rate and the maximal distribution distance. We investigate the imperfect quantum state preparation in Gaussian modulation coherent-state protocol both th...

[Phys. Rev. A 96, 042312] Published Wed Oct 11, 2017

Necessary condition for local distinguishability of maximally entangled states: Beyond orthogonality preservation


Author(s): Tanmay Singal, Ramij Rahaman, Sibasish Ghosh, and Guruprasad Kar

The (im)possibility of local distinguishability of orthogonal multipartite quantum states still remains an intriguing question. Beyond ${\mathbb{C}}^{3}⊗{\mathbb{C}}^{3}$, the problem remains unsolved even for maximally entangled states (MESs). So far, the only known condition for the local distingu...

[Phys. Rev. A 96, 042314] Published Wed Oct 11, 2017

Quantum annealing with a nonvanishing final value of the transverse field


Author(s): Kohji Nishimura and Hidetoshi Nishimori

We study the problem to infer the original ground state of a spin-glass Hamiltonian out of the information from the Hamiltonian with interactions deviated from the original ones. Our motivation comes from quantum annealing on a real device in which the values of interactions are degraded by noise. W...

[Phys. Rev. A 96, 042310] Published Tue Oct 10, 2017

High-fidelity Rydberg quantum gate via a two-atom dark state


Author(s): David Petrosyan, Felix Motzoi, Mark Saffman, and Klaus Mølmer

A modified Rydberg blockade gate that employs adiabatic following of a two-atom dark state is proposed. The scheme is resilient to the uncertainty in the interaction strength and can be employed to achieve fault-tolerant quantum computation with neutral atoms.

[Phys. Rev. A 96, 042306] Published Mon Oct 09, 2017

Noiseless attenuation using an optical parametric amplifier


Author(s): R. A. Brewster, I. C. Nodurft, T. B. Pittman, and J. D. Franson

The process of heralded noiseless amplification, and the inverse process of heralded noiseless attenuation, have potential applications in the context of quantum communications. Although several different physical implementations of heralded noiseless amplifiers have now been demonstrated, the resea...

[Phys. Rev. A 96, 042307] Published Mon Oct 09, 2017

Dissipative generation of a steady three-atom singlet state based on Rydberg pumping


Author(s): Xiang Chen, Hong Xie, Gong-Wei Lin, Xiao Shang, Ming-Yong Ye, and Xiu-Min Lin

Multiparticle singlet states are special quantum entangled states that have been shown to have many interesting applications. We develop a simple scheme to prepare a steady three-atom singlet state with a dissipative Rydberg pumping process, which combines dissipative dynamics and Rydberg interactio...

[Phys. Rev. A 96, 042308] Published Mon Oct 09, 2017

Benchmarking the state comparison amplifier


Author(s): Klaudia Kleczkowska, Ittoop Vergheese Puthoor, Lauren Bain, and Erika Andersson

The state comparison amplifier is a recently proposed probabilistic quantum amplifier, intended especially for amplifying coherent states. Its realization is simple and uses only linear optics and photodetectors, and the preparation of a “guess” state, typically a coherent state. Fidelity and succes...

[Phys. Rev. A 96, 042309] Published Mon Oct 09, 2017

Quantification of multidimensional entanglement stored in a crystal


Author(s): Alexey Tiranov, Sébastien Designolle, Emmanuel Zambrini Cruzeiro, Jonathan Lavoie, Nicolas Brunner, Mikael Afzelius, Marcus Huber, and Nicolas Gisin

The use of multidimensional entanglement opens new perspectives for quantum information processing. However, an important challenge in practice is to certify and characterize multidimensional entanglement from measurement data that are typically limited. Here, we report the certification and quantif...

[Phys. Rev. A 96, 040303(R)] Published Fri Oct 06, 2017

Second law of thermodynamics with quantum memory


Author(s): Li-Hang Ren and Heng Fan

We design a heat engine with multiheat reservoir, an ancillary system, and quantum memory. We then derive an inequality related to the second law of thermodynamics and give a limitation on the work gain from the engine by analyzing the entropy change and quantum mutual information change during the ...

[Phys. Rev. A 96, 042304] Published Fri Oct 06, 2017

Millimeter-wave interconnects for microwave-frequency quantum machines


Author(s): Marek Pechal and Amir H. Safavi-Naeini

Superconducting microwave circuits form a versatile platform for storing and manipulating quantum information. A major challenge to further scalability is to find approaches for connecting these systems over long distances and at high rates. One approach is to convert the quantum state of a microwav...

[Phys. Rev. A 96, 042305] Published Fri Oct 06, 2017

Hardness of classically sampling the one-clean-qubit model with constant total variation distance error


Author(s): Tomoyuki Morimae

The one-clean-qubit model (or the DQC1 model) is a restricted model of quantum computing where only a single input qubit is pure and all other input qubits are maximally mixed. In spite of the severe restriction, the model can solve several problems (such as calculating Jones polynomials) whose clas...

[Phys. Rev. A 96, 040302(R)] Published Thu Oct 05, 2017

Clustering in Hilbert space of a quantum optimization problem


Author(s): S. C. Morampudi, B. Hsu, S. L. Sondhi, R. Moessner, and C. R. Laumann

The solution space of many classical optimization problems breaks up into clusters which are extensively distant from one another in the Hamming metric. Here, we show that an analogous quantum clustering phenomenon takes place in the ground-state subspace of a certain quantum optimization problem. T...

[Phys. Rev. A 96, 042303] Published Thu Oct 05, 2017

Continuous-time quantum walks on spatially correlated noisy lattices


Author(s): Matteo A. C. Rossi, Claudia Benedetti, Massimo Borrelli, Sabrina Maniscalco, and Matteo G. A. Paris

We address memory effects and diffusive properties of a continuous-time quantum walk on a one-dimensional percolation lattice affected by spatially correlated random telegraph noise. In particular, by introducing spatially correlated time-dependent fluctuations in nearest-neighbor hopping amplitudes...

[Phys. Rev. A 96, 040301(R)] Published Wed Oct 04, 2017

Error rates and resource overheads of encoded three-qubit gates


Author(s): Ryuji Takagi, Theodore J. Yoder, and Isaac L. Chuang

A non-Clifford gate is required for universal quantum computation, and, typically, this is the most error-prone and resource-intensive logical operation on an error-correcting code. Small, single-qubit rotations are popular choices for this non-Clifford gate, but certain three-qubit gates, such as T...

[Phys. Rev. A 96, 042302] Published Wed Oct 04, 2017

Quenched dynamics of entangled states in correlated quantum dots


Author(s): N. S. Maslova, P. I. Arseyev, and V. N. Mantsevich

The time evolution of an initially prepared entangled state in the system of coupled quantum dots has been analyzed by means of two different theoretical approaches: equations of motion for all orders localized electron correlation functions, considering interference effects, and kinetic equations f...

[Phys. Rev. A 96, 042301] Published Mon Oct 02, 2017

Quantum microwave-optical interface with nitrogen-vacancy centers in diamond


Author(s): Bo Li, Peng-Bo Li, Yuan Zhou, Sheng-Li Ma, and Fu-Li Li

We propose an efficient scheme for a coherent quantum interface between microwave and optical photons using nitrogen-vacancy (NV) centers in diamond. In this setup, an NV center ensemble is simultaneously coupled to an optical and a microwave cavity. We show that, by using the collective spin excita...

[Phys. Rev. A 96, 032342] Published Fri Sep 29, 2017

Bayesian view of single-qubit clocks, and an energy versus accuracy tradeoff


Author(s): Manoj Gopalkrishnan, Varshith Kandula, Praveen Sriram, Abhishek Deshpande, and Bhaskaran Muralidharan

We bring a Bayesian approach to the analysis of clocks. Using exponential distributions as priors for clocks, we analyze how well one can keep time with a single qubit freely precessing under a magnetic field. We find that, at least with a single qubit, quantum mechanics does not allow exact timekee...

[Phys. Rev. A 96, 032339] Published Thu Sep 28, 2017

Classical capacity per unit cost for quantum channels


Author(s): Marcin Jarzyna

In most communication scenarios, sending a symbol encoded in a quantum state requires spending resources such as energy, which can be quantified by a cost of communication. A standard approach in this context is to quantify the performance of communication protocol by classical capacity, quantifying...

[Phys. Rev. A 96, 032340] Published Thu Sep 28, 2017

Fault tolerance with bare ancillary qubits for a [[7,1,3]] code


Author(s): Muyuan Li, Mauricio Gutiérrez, Stanley E. David, Alonzo Hernandez, and Kenneth R. Brown

We present a $[[7,1,3]]$ quantum error-correcting code that is able to achieve fault-tolerant syndrome measurement using one ancillary qubit per stabilizer for an error model of independent single-qubit Pauli errors. All single-qubit Pauli errors on the ancillary qubits propagate to form exclusively...

[Phys. Rev. A 96, 032341] Published Thu Sep 28, 2017

Nonuniform code concatenation for universal fault-tolerant quantum computing


Author(s): Eesa Nikahd, Mehdi Sedighi, and Morteza Saheb Zamani

Using transversal gates is a straightforward and efficient technique for fault-tolerant quantum computing. Since transversal gates alone cannot be computationally universal, they must be combined with other approaches such as magic state distillation, code switching, or code concatenation to achieve...

[Phys. Rev. A 96, 032337] Published Wed Sep 27, 2017

Proposal for a minimal surface code experiment


Author(s): James R. Wootton, Andreas Peter, János R. Winkler, and Daniel Loss

Current quantum technology is approaching the system sizes and fidelities required for quantum error correction. It is therefore important to determine exactly what is needed for proof-of-principle experiments, which will be a major step towards fault-tolerant quantum computation. Here we propose a ...

[Phys. Rev. A 96, 032338] Published Wed Sep 27, 2017

Verifiable fault tolerance in measurement-based quantum computation


Author(s): Keisuke Fujii and Masahito Hayashi

Quantum systems, in general, cannot be simulated efficiently by a classical computer, and hence are useful for solving certain mathematical problems and simulating quantum many-body systems. This also implies, unfortunately, that verification of the output of the quantum systems is not so trivial, s...

[Phys. Rev. A 96, 030301(R)] Published Mon Sep 25, 2017

Quantum coherences of indistinguishable particles


Author(s): Jan Sperling, Armando Perez-Leija, Kurt Busch, and Ian A. Walmsley

We study different notions of quantum correlations in multipartite systems of distinguishable and indistinguishable particles. Based on the definition of quantum coherence for a single particle, we consider two possible extensions of this concept to the many-particle scenario and determine the influ...

[Phys. Rev. A 96, 032334] Published Mon Sep 25, 2017

Analytic next-to-nearest-neighbor $XX$ models with perfect state transfer and fractional revival


Author(s): Matthias Christandl, Luc Vinet, and Alexei Zhedanov

Certain nonuniformly coupled spin chains can exhibit perfect transfer of quantum states from end to end. Motivated by recent experimental implementations in evanescently coupled waveguide arrays, we extend the simplest such chain to next-to-nearest-neighbor couplings. It is shown analytically that p...

[Phys. Rev. A 96, 032335] Published Mon Sep 25, 2017

Implementing stabilizer codes in noisy environments


Author(s): Jie Song, Chuang Li, Zi-Jing Zhang, Yong-Yuan Jiang, and Yan Xia

We propose an effective approach to implement stabilizer codes by using Rydberg blockade in open systems. Along the dynamics pathway toward the doubly Rydberg excited states, it is shown that an arbitrary initial state can be driven to multibody entanglement via stabilizer codes with the help of ato...

[Phys. Rev. A 96, 032336] Published Mon Sep 25, 2017

Aggregating quantum repeaters for the quantum internet


Author(s): Koji Azuma and Go Kato

The quantum internet holds promise for accomplishing quantum teleportation and unconditionally secure communication freely between arbitrary clients all over the globe, as well as the simulation of quantum many-body systems. For such a quantum internet protocol, a general fundamental upper bound on ...

[Phys. Rev. A 96, 032332] Published Fri Sep 22, 2017

Entanglement generation between a charge qubit and its bosonic environment during pure dephasing: Dependence on the environment size


Author(s): Tymoteusz Salamon and Katarzyna Roszak

We study entanglement generated between a charge qubit and a bosonic bath due to their joint evolution which leads to pure dephasing of the qubit. We tune the parameters of the interaction, so that the decoherence is quantitatively independent of the number of bosonic modes taken into account and in...

[Phys. Rev. A 96, 032333] Published Fri Sep 22, 2017

Semiclassical formulation of the Gottesman-Knill theorem and universal quantum computation


Author(s): Lucas Kocia, Yifei Huang, and Peter Love

We give a path-integral formulation of the time evolution of qudits of odd dimension. This allows us to consider semiclassical evolution of discrete systems in terms of an expansion of the propagator in powers of $ℏ$. The largest power of $ℏ$ required to describe the evolution is a traditional measu...

[Phys. Rev. A 96, 032331] Published Wed Sep 20, 2017

Graph-associated entanglement cost of a multipartite state in exact and finite-block-length approximate constructions


Author(s): Hayata Yamasaki, Akihito Soeda, and Mio Murao

We introduce and analyze graph-associated entanglement cost, a generalization of the entanglement cost of quantum states to multipartite settings. We identify a necessary and sufficient condition for any multipartite entangled state to be constructible when quantum communication between the multiple...

[Phys. Rev. A 96, 032330] Published Tue Sep 19, 2017

Entanglement enhancement through multirail noise reduction for continuous-variable measurement-based quantum-information processing


Author(s): Yung-Chao Su and Shin-Tza Wu

We study theoretically the teleportation of a controlled-phase (cz) gate through measurement-based quantum-information processing for continuous-variable systems. We examine the degree of entanglement in the output modes of the teleported cz-gate for two classes of resource states: the canonical clu...

[Phys. Rev. A 96, 032327] Published Mon Sep 18, 2017

Tunable quantum entanglement of three qubits in a nonstationary cavity


Author(s): Mirko Amico, Oleg L. Berman, and Roman Ya. Kezerashvili

We investigate the tunable quantum entanglement and the probabilities of excitations in a system of three qubits in a nonstationary cavity due to the dynamical Lamb effect, caused by nonadiabatic fast change of the boundary conditions of the cavity. The transition amplitudes and the probabilities of...

[Phys. Rev. A 96, 032328] Published Mon Sep 18, 2017

Proposal for automated transformations on single-photon multipath qudits


Author(s): R. D. Baldijão, G. F. Borges, B. Marques, M. A. Solís-Prosser, L. Neves, and S. Pádua

We propose a method for implementing automated state transformations on single-photon multipath qudits encoded in a one-dimensional transverse spatial domain. It relies on transferring the encoding from this domain to the orthogonal one by applying a spatial phase modulation with diffraction grating...

[Phys. Rev. A 96, 032329] Published Mon Sep 18, 2017

Exact sampling hardness of Ising spin models


Author(s): B. Fefferman, M. Foss-Feig, and A. V. Gorshkov

We study the complexity of classically sampling from the output distribution of an Ising spin model, which can be implemented naturally in a variety of atomic, molecular, and optical systems. In particular, we construct a specific example of an Ising Hamiltonian that, after time evolution starting f...

[Phys. Rev. A 96, 032324] Published Thu Sep 14, 2017

Nonlocal bunching of composite bosons


Author(s): Zakarya Lasmar, Dagomir Kaszlikowski, and Paweł Kurzyński

It was suggested that two entangled fermions can behave like a single boson and that the bosonic quality is proportional to the degree of entanglement between the two particles. The relation between bosonic quality and entanglement is quite natural if one takes into account the fact that entanglemen...

[Phys. Rev. A 96, 032325] Published Thu Sep 14, 2017

Boson sampling with Gaussian measurements


Author(s): L. Chakhmakhchyan and N. J. Cerf

We develop an alternative boson sampling model operating on single-photon states followed by linear interferometry and Gaussian measurements. The hardness proof for simulating such continuous-variable measurements is established in two main steps, making use of the symmetry of quantum evolution unde...

[Phys. Rev. A 96, 032326] Published Thu Sep 14, 2017

Finding paths with quantum walks or quantum walking through a maze


Author(s): Daniel Reitzner, Mark Hillery, and Daniel Koch

We show that it is possible to use a quantum walk to find a path from one marked vertex to another. In the specific case of $M$ stars connected in a chain, one can find the path from the first star to the last one in $O(M\sqrt{N})$ steps, where $N$ is the number of spokes of each star. First we prov...

[Phys. Rev. A 96, 032323] Published Wed Sep 13, 2017

General bounds for sender-receiver capacities in multipoint quantum communications


Author(s): Riccardo Laurenza and Stefano Pirandola

We investigate the maximum rates for transmitting quantum information, distilling entanglement, and distributing secret keys between a sender and a receiver in a multipoint communication scenario, with the assistance of unlimited two-way classical communication involving all parties. First we consid...

[Phys. Rev. A 96, 032318] Published Tue Sep 12, 2017

Discrete-to-continuous transition in quantum phase estimation


Author(s): Wojciech Rządkowski and Rafał Demkowicz-Dobrzański

We analyze the problem of quantum phase estimation in which the set of allowed phases forms a discrete $N$-element subset of the whole $[0,2π]$ interval, ${φ}_{n}=2πn/N, n=0,⋯,N−1$, and study the discrete-to-continuous transition $N→∞$ for various cost functions as well as the mutual information. We...

[Phys. Rev. A 96, 032319] Published Tue Sep 12, 2017

Quantum interferometry in multimode systems


Author(s): J. Chwedeńczuk

We consider the situation when the signal propagating through each arm of an interferometer has a complicated multimode structure. We demonstrate that the shot-noise level for such a setup is the same as for the common two-mode case for as long as the interferometric transformation treats each arm a...

[Phys. Rev. A 96, 032320] Published Tue Sep 12, 2017

Nonunitary quantum computation in the ground space of local Hamiltonians


Author(s): Naïri Usher, Matty J. Hoban, and Dan E. Browne

A central result in the study of quantum Hamiltonian complexity is that the $k$-local Hamiltonian problem is quantum-Merlin-Arthur–complete. In that problem, we must decide if the lowest eigenvalue of a Hamiltonian is bounded below some value, or above another, promised one of these is true. Given t...

[Phys. Rev. A 96, 032321] Published Tue Sep 12, 2017

Genuinely entangled symmetric states with no $N$-partite correlations


Author(s): S. Designolle, O. Giraud, and J. Martin

We investigate genuinely entangled $N$-qubit states with no $N$-partite correlations in the case of symmetric states. Using a tensor representation for mixed symmetric states, we obtain a simple characterization of the absence of $N$-partite correlations. We show that symmetric states with no $N$-pa...

[Phys. Rev. A 96, 032322] Published Tue Sep 12, 2017

Entanglement and the truncated moment problem


Author(s): F. Bohnet-Waldraff, D. Braun, and O. Giraud

We map the quantum entanglement problem onto the mathematically well-studied truncated moment problem. This yields a necessary and sufficient condition for separability that can be checked by a hierarchy of semidefinite programs. The algorithm always gives a certificate of entanglement if the state ...

[Phys. Rev. A 96, 032312] Published Mon Sep 11, 2017

Quantum uncertainty relation using coherence


Author(s): Xiao Yuan, Ge Bai, Tianyi Peng, and Xiongfeng Ma

Measurement outcomes of a quantum state can be genuinely random (unpredictable) according to the basic laws of quantum mechanics. The Heisenberg-Robertson uncertainty relation puts constraints on the accuracy of two noncommuting observables. The existing uncertainty relations adopt variance or entro...

[Phys. Rev. A 96, 032313] Published Mon Sep 11, 2017

Arbitrary nuclear-spin gates in diamond mediated by a nitrogen-vacancy-center electron spin


Author(s): J. Casanova, Z.-Y. Wang, and M. B. Plenio

We show that arbitrary $N$-qubit interactions among nuclear spins can be achieved efficiently in solid state quantum platforms, such as nitrogen vacancy centers in diamond, by exerting control only on the electron spin coupled to the nuclei. This allows to exploit nuclear spins as robust quantum reg...

[Phys. Rev. A 96, 032314] Published Mon Sep 11, 2017

Disorder-assisted distribution of entanglement in $XY$ spin chains


Author(s): Guilherme M. A. Almeida, Francisco A. B. F. de Moura, Tony J. G. Apollaro, and Marcelo L. Lyra

We study the creation and distribution of entanglement in disordered $XY$-type spin-$1/2$ chains for the paradigmatic case of a single flipped spin prepared on a fully polarized background. The local magnetic field is set to follow a disordered long-range-correlated sequence with power-law spectrum....

[Phys. Rev. A 96, 032315] Published Mon Sep 11, 2017

Operational one-to-one mapping between coherence and entanglement measures


Author(s): Huangjun Zhu, Zhihao Ma, Zhu Cao, Shao-Ming Fei, and Vlatko Vedral

We establish a general operational one-to-one mapping between coherence measures and entanglement measures: Any entanglement measure of bipartite pure states is the minimum of a suitable coherence measure over product bases. Any coherence measure of pure states, with extension to mixed states by con...

[Phys. Rev. A 96, 032316] Published Mon Sep 11, 2017

Universal measurement-based quantum computation in two-dimensional symmetry-protected topological phases


Author(s): Tzu-Chieh Wei and Ching-Yu Huang

Recent progress in the characterization of gapped quantum phases has also triggered the search for a universal resource for quantum computation in symmetric gapped phases. Prior works in one dimension suggest that it is a feature more common than previously thought, in that nontrivial one-dimensiona...

[Phys. Rev. A 96, 032317] Published Mon Sep 11, 2017

Controlled generation of mixed spatial qudits with arbitrary degree of purity


Author(s): J. J. M. Varga, S. Ledesma, C. Iemmi, and L. Rebón

We propose a method for preparing mixed quantum states of arbitrary dimension $D$ ($D≥2$) which are codified in the discretized transverse momentum and position of single photons, once they are sent through an aperture with $D$ slits. Following our previous technique we use a programmable single pha...

[Phys. Rev. A 96, 032309] Published Fri Sep 08, 2017

Control methods for improved Fisher information with quantum sensing


Author(s): Tuvia Gefen, Fedor Jelezko, and Alex Retzker

Recently new approaches for sensing the frequency of time dependent Hamiltonians have been presented, and it was shown that the optimal Fisher information scales as ${T}^{4}.$ We present here our interpretation of this new scaling, where the relative phase is accumulated quadratically with time, and...

[Phys. Rev. A 96, 032310] Published Fri Sep 08, 2017

Convex approximations of quantum channels


Author(s): Massimiliano F. Sacchi and Tito Sacchi

We address the problem of optimally approximating the action of a desired and unavailable quantum channel $\mathrm{Φ}$ having at our disposal a single use of a given set of other channels ${{\mathrm{Ψ}}_{i}}$. The problem is recast to look for the least distinguishable channel from $\mathrm{Φ}$ amon...

[Phys. Rev. A 96, 032311] Published Fri Sep 08, 2017

Displaced photon-number entanglement tests


Author(s): B. Kühn, W. Vogel, and J. Sperling

Based on correlations of coherently displaced photon numbers, we derive entanglement criteria for the purpose of verifying non-Gaussian entanglement. Our construction method enables us to verify bipartite and multipartite entanglement of complex states of light. An important advantage of our techniq...

[Phys. Rev. A 96, 032306] Published Wed Sep 06, 2017

Optimal design of measurement settings for quantum-state-tomography experiments


Author(s): Jun Li, Shilin Huang, Zhihuang Luo, Keren Li, Dawei Lu, and Bei Zeng

Quantum state tomography is an indispensable but costly part of many quantum experiments. Typically, it requires measurements to be carried out in a number of different settings on a fixed experimental setup. The collected data are often informationally overcomplete, with the amount of information r...

[Phys. Rev. A 96, 032307] Published Wed Sep 06, 2017

Implementing the sine transform of fermionic modes as a tensor network


Author(s): Hannes Epple, Pascal Fries, and Haye Hinrichsen

Based on the algebraic theory of signal processing, we recursively decompose the discrete sine transform of the first kind (DST-I) into small orthogonal block operations. Using a diagrammatic language, we then second-quantize this decomposition to construct a tensor network implementing the DST-I fo...

[Phys. Rev. A 96, 032308] Published Wed Sep 06, 2017

Quantum centrality testing on directed graphs via $PT$-symmetric quantum walks


Author(s): J. A. Izaac, J. B. Wang, P. C. Abbott, and X. S. Ma

Various quantum-walk-based algorithms have been proposed to analyze and rank the centrality of graph vertices. However, issues arise when working with directed graphs: the resulting non-Hermitian Hamiltonian leads to nonunitary dynamics, and the total probability of the quantum walker is no longer c...

[Phys. Rev. A 96, 032305] Published Tue Sep 05, 2017

Quantum algorithm for support matrix machines


Author(s): Bojia Duan, Jiabin Yuan, Ying Liu, and Dan Li

We propose a quantum algorithm for support matrix machines (SMMs) that efficiently addresses an image classification problem by introducing a least-squares reformulation. This algorithm consists of two core subroutines: a quantum matrix inversion (Harrow-Hassidim-Lloyd, HHL) algorithm and a quantum ...

[Phys. Rev. A 96, 032301] Published Fri Sep 01, 2017

Multipartite entanglement from matrix-product states and a quantum phase transition


Author(s): Guo-Qing Zhang, Wei Wu, and Jing-Bo Xu

We investigate multipartite entanglement and a quantum phase transition for spin chain systems by making use of the density-matrix renormalization-group method in the form of matrix-product states. It is found that multipartite entanglement changes dramatically near the critical region and the resid...

[Phys. Rev. A 96, 032302] Published Fri Sep 01, 2017

Engineered noisy environment for studying decoherence


Author(s): Ai Iwakura, Yuichiro Matsuzaki, and Yasushi Kondo

The largest obstacle to perform quantum information processing is decoherence of a system. In order to overcome this, various techniques, such as dynamical decoupling and quantum Zeno effects, have been proposed and demonstrated. Here, we present an NMR model with which various decoherence suppressi...

[Phys. Rev. A 96, 032303] Published Fri Sep 01, 2017

Anticoherence measures for pure spin states


Author(s): D. Baguette and J. Martin

The set of pure spin states with vanishing spin expectation value can be regarded as the set of the less coherent pure spin states. This set can be divided into a finite number of nested subsets on the basis of higher order moments of the spin operators. This subdivision relies on the notion of anti...

[Phys. Rev. A 96, 032304] Published Fri Sep 01, 2017

Quantum-inspired algorithm for estimating the permanent of positive semidefinite matrices


Author(s): L. Chakhmakhchyan, N. J. Cerf, and R. Garcia-Patron

We construct a quantum-inspired classical algorithm for computing the permanent of Hermitian positive semidefinite matrices by exploiting a connection between these mathematical structures and the boson sampling model. Specifically, the permanent of a Hermitian positive semidefinite matrix can be ex...

[Phys. Rev. A 96, 022329] Published Thu Aug 31, 2017

Efficient $Z$ gates for quantum computing


Author(s): David C. McKay, Christopher J. Wood, Sarah Sheldon, Jerry M. Chow, and Jay M. Gambetta

For superconducting qubits, microwave pulses drive rotations around the Bloch sphere. The phase of these drives can be used to generate zero-duration arbitrary virtual $Z$ gates, which, combined with two ${X}_{π/2}$ gates, can generate any SU(2) gate. Here we show how to best utilize these virtual $...

[Phys. Rev. A 96, 022330] Published Thu Aug 31, 2017

Design method of dynamical decoupling sequences integrated with optimal control theory


Author(s): Yutaka Tabuchi, Makoto Negoro, and Masahiro Kitagawa

A method for synthesizing dynamical decoupling (DD) sequences is presented, which can tailor these sequences to a given set of qubits, environments, instruments, and available resources using partial information of the system. The key concept behind the generation of the DD sequences involves not on...

[Phys. Rev. A 96, 022331] Published Thu Aug 31, 2017

Conditional mutual information and quantum steering


Author(s): Eneet Kaur, Xiaoting Wang, and Mark M. Wilde

Quantum steering has recently been formalized in the framework of a resource theory of steering, and several quantifiers have already been introduced. Here, we propose an information-theoretic quantifier for steering called intrinsic steerability, which uses conditional mutual information to measure...

[Phys. Rev. A 96, 022332] Published Thu Aug 31, 2017

Geometric multiaxial representation of $N$-qubit mixed symmetric separable states


Author(s): Suma SP, Swarnamala Sirsi, Subramanya Hegde, and Karthik Bharath

The study of $N$-qubit mixed symmetric separable states is a longstanding challenging problem as no unique separability criterion exists. In this regard, we take up the $N$-qubit mixed symmetric separable states for a detailed study as these states are of experimental importance and offer an elegant...

[Phys. Rev. A 96, 022328] Published Wed Aug 30, 2017

State protection by quantum control before and after noise processes


Author(s): Hiroaki Wakamura, Ryûitirô Kawakubo, and Tatsuhiko Koike

We discuss protection of a quantum state that goes through a noise process by measurements and operations before and after the noise process. In our previous work, we showed the nonexistence of “truly quantum” protocols that protect an unknown qubit state against depolarizing noise better than “clas...

[Phys. Rev. A 96, 022325] Published Tue Aug 29, 2017

Direct comparison of quantum and simulated annealing on a fully connected Ising ferromagnet


Author(s): Matteo M. Wauters, Rosario Fazio, Hidetoshi Nishimori, and Giuseppe E. Santoro

We compare the performance of quantum annealing (QA, through Schrödinger dynamics) and simulated annealing (SA, through a classical master equation) on the $p$-spin infinite range ferromagnetic Ising model, by slowly driving the system across its equilibrium, quantum or classical, phase transition. ...

[Phys. Rev. A 96, 022326] Published Tue Aug 29, 2017

Optimal quantum operations at zero energy cost


Author(s): Giulio Chiribella and Yuxiang Yang

Quantum technologies are developing powerful tools to generate and manipulate coherent superpositions of different energy levels. Envisaging a new generation of energy-efficient quantum devices, here we explore how coherence can be manipulated without exchanging energy with the surrounding environme...

[Phys. Rev. A 96, 022327] Published Tue Aug 29, 2017

Work sharing of qubits in topological error corrections


Author(s): Tetsufumi Tanamoto and Hayato Goto

Topological error-correcting codes, such as surface codes and color codes, are promising because quantum operations are realized by two-dimensionally (2D) arrayed quantum bits (qubits). However, physical wiring of electrodes to qubits is complicated, and 3D integration for the wiring requires furthe...

[Phys. Rev. A 96, 022324] Published Mon Aug 28, 2017

Simulation of non-Pauli channels


Author(s): Thomas P. W. Cope, Leon Hetzel, Leonardo Banchi, and Stefano Pirandola

We consider the simulation of a quantum channel by two parties who share a resource state and may apply local operations assisted by classical communication (LOCC). One specific type of such LOCC is standard teleportation, which is however limited to the simulation of Pauli channels. Here we show ho...

[Phys. Rev. A 96, 022323] Published Fri Aug 25, 2017

Rydberg-interaction gates via adiabatic passage and phase control of driving fields


Author(s): Huaizhi Wu, Xi-Rong Huang, Chang-Sheng Hu, Zhen-Biao Yang, and Shi-Biao Zheng

In this paper we propose two theoretical schemes for implementation of quantum phase gates by engineering the phase-sensitive dark state of two atoms subjected to Rydberg-Rydberg interaction. Combining the conventional adiabatic techniques and currently developed approaches of phase control, a feasi...

[Phys. Rev. A 96, 022321] Published Wed Aug 23, 2017

Amending entanglement-breaking channels via intermediate unitary operations


Author(s): Á. Cuevas, A. De Pasquale, A. Mari, A. Orieux, S. Duranti, M. Massaro, A. Di Carli, E. Roccia, J. Ferraz, F. Sciarrino, P. Mataloni, and V. Giovannetti

We report a bulk optics experiment demonstrating the possibility of restoring the entanglement distribution through noisy quantum channels by inserting a suitable unitary operation (filter) in the middle of the transmission process. We focus on two relevant classes of single-qubit channels consistin...

[Phys. Rev. A 96, 022322] Published Wed Aug 23, 2017

All entangled pure quantum states violate the bilocality inequality


Author(s): Nicolas Gisin, Quanxin Mei, Armin Tavakoli, Marc Olivier Renou, and Nicolas Brunner

A thorough characterization of bilocality in quantum networks is set forward, providing important results for the development of device-independent quantum information processing.

[Phys. Rev. A 96, 020304(R)] Published Tue Aug 22, 2017

Hyperentangled Bell-state analysis and hyperdense coding assisted by auxiliary entanglement


Author(s): Xi-Han Li and Shohini Ghose

We present a technique for hyperentangled Bell-state analysis that only relies on linear optics and is assisted by auxiliary entangled states. This technique can be used to implement hyperdense coding with an experimentally realizable two-photon state hyperentangled in polarization and two longitudi...

[Phys. Rev. A 96, 020303(R)] Published Mon Aug 21, 2017

$N$ identical particles and one particle to entangle them all


Author(s): Bruno Bellomo, Rosario Lo Franco, and Giuseppe Compagno

In quantum information, $W$ states are a central class of multipartite entangled states because of their robustness against noise and their use in many quantum processes. Their generation, however, remains a demanding task whose difficulty increases with the number of particles. We report a simple s...

[Phys. Rev. A 96, 022319] Published Mon Aug 21, 2017

Entanglement-distillation attack on continuous-variable quantum key distribution in a turbulent atmospheric channel


Author(s): Ying Guo, Cailang Xie, Qin Liao, Wei Zhao, Guihua Zeng, and Duan Huang

The survival of Gaussian quantum states in a turbulent atmospheric channel is of crucial importance in free-space continuous-variable (CV) quantum key distribution (QKD), in which the transmission coefficient will fluctuate in time, thus resulting in non-Gaussian quantum states. Different from quant...

[Phys. Rev. A 96, 022320] Published Mon Aug 21, 2017

High-dimensional decoy-state quantum key distribution over multicore telecommunication fibers


Author(s): G. Cañas, N. Vera, J. Cariñe, P. González, J. Cardenas, P. W. R. Connolly, A. Przysiezna, E. S. Gómez, M. Figueroa, G. Vallone, P. Villoresi, T. Ferreira da Silva, G. B. Xavier, and G. Lima

Multiplexing is a strategy to augment the transmission capacity of a communication system. It consists of combining multiple signals over the same data channel and it has been very successful in classical communications. However, the use of enhanced channels has only reached limited practicality in ...

[Phys. Rev. A 96, 022317] Published Fri Aug 18, 2017

Optimal sequential state discrimination between two mixed quantum states


Author(s): Min Namkung and Younghun Kwon

Recently, sequential state discrimination, as a quantum-key distribution protocol, has been proposed for multiple receivers. A previous study [J. A. Bergou et al., Phys. Rev. Lett. 111, 100501 (2013)] showed that every receiver could successfully perform a sequential state discrimination of two pur...

[Phys. Rev. A 96, 022318] Published Fri Aug 18, 2017

Practical issues in decoy-state quantum key distribution based on the central limit theorem


Author(s): A. S. Trushechkin, E. O. Kiktenko, and A. K. Fedorov

Decoy-state quantum key distribution (QKD) is a standard tool for long-distance quantum communications. An important issue in this field is processing the decoy-state statistics taking into account statistical fluctuations (or “finite-key effects”). In this work, we propose and analyze an option for...

[Phys. Rev. A 96, 022316] Published Thu Aug 17, 2017

Probabilistic quantum teleportation via thermal entanglement


Author(s): Raphael Fortes and Gustavo Rigolin

We study the probabilistic (conditional) teleportation protocol when the entanglement needed for its implementation is given by thermal entanglement, i.e., when the entangled resource connecting Alice and Bob is an entangled mixed state described by the canonical ensemble density matrix. Specificall...

[Phys. Rev. A 96, 022315] Published Wed Aug 16, 2017

Quantum illumination for enhanced detection of Rayleigh-fading targets


Author(s): Quntao Zhuang, Zheshen Zhang, and Jeffrey H. Shapiro

Quantum illumination (QI) is an entanglement-enhanced sensing system whose performance advantage over a comparable classical system survives its usage in an entanglement-breaking scenario plagued by loss and noise. In particular, QI's error-probability exponent for discriminating between equally lik...

[Phys. Rev. A 96, 020302(R)] Published Tue Aug 15, 2017

Fast quantum state engineering via universal SU(2) transformation


Author(s): Bi-Hua Huang, Yi-Hao Kang, Ye-Hong Chen, Qi-Cheng Wu, Jie Song, and Yan Xia

We introduce a simple yet versatile protocol to inverse engineer the time-dependent Hamiltonian in two- and three-level systems. In the protocol, by utilizing a universal SU(2) transformation, a given speedup goal can be obtained with large freedom to select the control parameters. As an illustratio...

[Phys. Rev. A 96, 022314] Published Tue Aug 15, 2017

Linear feedback stabilization of a dispersively monitored qubit


Author(s): Taylor Lee Patti, Areeya Chantasri, Luis Pedro García-Pintos, Andrew N. Jordan, and Justin Dressel

The state of a continuously monitored qubit evolves stochastically, exhibiting competition between coherent Hamiltonian dynamics and diffusive partial collapse dynamics that follow the measurement record. We couple these distinct types of dynamics together by linearly feeding the collected record fo...

[Phys. Rev. A 96, 022311] Published Mon Aug 14, 2017

Optimal discrimination of single-qubit mixed states


Author(s): Graeme Weir, Stephen M. Barnett, and Sarah Croke

We consider the problem of minimum-error quantum state discrimination for single-qubit mixed states. We present a method which uses the Helstrom conditions constructively and analytically; this algebraic approach is complementary to existing geometric methods, and solves the problem for any number o...

[Phys. Rev. A 96, 022312] Published Mon Aug 14, 2017

Monogamy inequalities for certifiers of continuous-variable Einstein-Podolsky-Rosen entanglement without the assumption of Gaussianity


Author(s): L. Rosales-Zárate, R. Y. Teh, B. Opanchuk, and M. D. Reid

We consider three modes $A$, $B$, and $C$ and derive monogamy inequalities that constrain the distribution of bipartite continuous variable Einstein-Podolsky-Rosen entanglement amongst the three modes. The inequalities hold without the assumption of Gaussian states, and are based on measurements of ...

[Phys. Rev. A 96, 022313] Published Mon Aug 14, 2017

Secure alignment of coordinate systems using quantum correlation


Author(s): F. Rezazadeh, A. Mani, and V. Karimipour

We show that two parties far apart can use shared entangled states and classical communication to align their coordinate systems with a very high fidelity. Moreover, compared with previous methods proposed for such a task, i.e., sending parallel or antiparallel pairs or groups of spin states, our me...

[Phys. Rev. A 96, 022310] Published Fri Aug 11, 2017

Robust not gate by single-shot-shaped pulses: Demonstration of the efficiency of the pulses in rephasing atomic coherences


Author(s): Leo Van-Damme, Daniel Schraft, Genko T. Genov, Dominique Sugny, Thomas Halfmann, and Stéphane Guérin

We derive a versatile protocol to implement a fast and robust not quantum gate, driven by single-shot-shaped pulses with appropriate time-dependent phase and intensity profiles. The pulses are derived by combining analytic computations and numerical optimizations. We experimentally demonstrate the a...

[Phys. Rev. A 96, 022309] Published Thu Aug 10, 2017

Qubit entanglement across $ε$-near-zero media


Author(s): S.-A. Biehs and G. S. Agarwal

Currently, epsilon-near-zero (ENZ) materials have become important for controlling the propagation of light and enhancing by several orders of magnitude the Kerr and other nonlinearities. Given this advance it is important to examine the quantum electrodynamic processes and information tasks near EN...

[Phys. Rev. A 96, 022308] Published Wed Aug 09, 2017