PRA: Quantum information

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Recently published articles in Phys. Rev. A in the Table of Content section "Quantum information"
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Convexity properties of superpositions of degenerate bipartite eigenstates

Fri, 2019-05-24 12:00

Author(s): Natalia Giovenale, Federico M. Pont, Pablo Serra, and Omar Osenda

The entanglement content of superpositions of pairs of degenerate eigenstates of a bipartite system is considered in the case that both eigenstates are also eigenstates of the z component of the total angular momentum. It is shown that the von Neumann entropy of the state that is obtained tracing ou...


[Phys. Rev. A 99, 052340] Published Fri May 24, 2019

Categories: Journals, Physics

Minimal nonorthogonal gate decomposition for qubits with limited control

Fri, 2019-05-24 12:00

Author(s): Xiao-Ming Zhang, Jianan Li, Xin Wang, and Man-Hong Yung

In quantum control theory, a question of fundamental and practical interest is how an arbitrary unitary transformation can be decomposed into a minimum number of elementary rotations for implementation, subject to various physical constraints. Examples include the singlet-triplet (ST) and exchange-o...


[Phys. Rev. A 99, 052339] Published Fri May 24, 2019

Categories: Journals, Physics

Digitization of scalar fields for quantum computing

Thu, 2019-05-23 12:00

Author(s): Natalie Klco and Martin J. Savage

Qubit, operator, and gate resources required for the digitization of lattice λϕ4 scalar field theories onto quantum computers are considered, building upon the foundational work by Jordan et al. [Quantum Inf. Comput. 14, 1014 (2014); Science 336, 1130 (2012)], with a focus towards noisy intermediate...


[Phys. Rev. A 99, 052335] Published Thu May 23, 2019

Categories: Journals, Physics

Quantifying entanglement of formation for two-mode Gaussian states: Analytical expressions for upper and lower bounds and numerical estimation of its exact value

Thu, 2019-05-23 12:00

Author(s): Spyros Tserkis, Sho Onoe, and Timothy C. Ralph

Entanglement of formation quantifies the entanglement of a state in terms of the entropy of entanglement of the least entangled pure state needed to prepare it. An analytical expression for this measure exists only for special cases, and finding a closed formula for an arbitrary state remains an ope...


[Phys. Rev. A 99, 052337] Published Thu May 23, 2019

Categories: Journals, Physics

Upper bound on certifiable randomness from a quantum black-box device

Thu, 2019-05-23 12:00

Author(s): Marie Ioannou, Jonatan Bohr Brask, and Nicolas Brunner

Quantum theory allows for randomness generation in a device-independent setting, where no detailed description of the experimental device is required. Here we derive a general upper bound on the amount of randomness that can be certified in such a setting. Our bound applies to any black-box scenario...


[Phys. Rev. A 99, 052338] Published Thu May 23, 2019

Categories: Journals, Physics

Structure of minimum error discrimination for linearly independent states

Thu, 2019-05-23 12:00

Author(s): Tanmay Singal, Eunsang Kim, and Sibasish Ghosh

In this paper we study the minimum error discrimination problem (MED) for ensembles of linearly independent (LI) states. We define a bijective map from the set of those ensembles to itself and we show that the pretty good measurement (PGM) and the optimal measurement for the MED are related by the m...


[Phys. Rev. A 99, 052334] Published Thu May 23, 2019

Categories: Journals, Physics

Optimal realistic attacks in continuous-variable quantum key distribution

Thu, 2019-05-23 12:00

Author(s): Nedasadat Hosseinidehaj, Nathan Walk, and Timothy C. Ralph

Quantum cryptographic protocols are typically analyzed by assuming that potential opponents can carry out all physical operations, an assumption which grants capabilities far in excess of present technology. Adjusting this assumption to reflect more realistic capabilities is an attractive prospect, ...


[Phys. Rev. A 99, 052336] Published Thu May 23, 2019

Categories: Journals, Physics

Near-term quantum-repeater experiments with nitrogen-vacancy centers: Overcoming the limitations of direct transmission

Wed, 2019-05-22 12:00

Author(s): Filip Rozpędek, Raja Yehia, Kenneth Goodenough, Maximilian Ruf, Peter C. Humphreys, Ronald Hanson, Stephanie Wehner, and David Elkouss

Quantum channels enable the implementation of communication tasks inaccessible to their classical counterparts. The most famous example is the distribution of secret key. However, in the absence of quantum repeaters, the rate at which these tasks can be performed is dictated by the losses in the qua...


[Phys. Rev. A 99, 052330] Published Wed May 22, 2019

Categories: Journals, Physics

Ultrafast variational simulation of nontrivial quantum states with long-range interactions

Wed, 2019-05-22 12:00

Author(s): Wen Wei Ho, Cheryne Jonay, and Timothy H. Hsieh

State preparation protocols ideally require as minimal operations as possible in order to be implemented in near-term, potentially noisy quantum devices. Motivated by long-range interactions (LRIs) intrinsic to many present-day experimental platforms (trapped ions, Rydberg atom arrays, etc.), we inv...


[Phys. Rev. A 99, 052332] Published Wed May 22, 2019

Categories: Journals, Physics

Quantum-assisted Gaussian process regression

Wed, 2019-05-22 12:00

Author(s): Zhikuan Zhao, Jack K. Fitzsimons, and Joseph F. Fitzsimons

Gaussian processes (GPs) are a widely used model for regression problems in supervised machine learning. Implementation of GP regression typically requires O(n3) logic gates. We show that the quantum linear systems algorithm [Harrow et al., Phys. Rev. Lett. 103, 150502 (2009)] can be applied to Gaus...


[Phys. Rev. A 99, 052331] Published Wed May 22, 2019

Categories: Journals, Physics

Optimal quantum subsystem codes in two dimensions

Wed, 2019-05-22 12:00

Author(s): Theodore J. Yoder

Given any two classical codes with parameters [n1,k,d1] and [n2,k,d2], we show how to construct a quantum subsystem code in two dimensions with parameters [[N,K,D]] satisfying N≤2n1n2, K=k, and D=min(d1,d2). These quantum codes are in the class of generalized Bacon-Shor codes introduced by Bravyi [P...


[Phys. Rev. A 99, 052333] Published Wed May 22, 2019

Categories: Journals, Physics

Framework for covert and secret key expansion over classical-quantum channels

Mon, 2019-05-20 12:00

Author(s): Mehrdad Tahmasbi and Matthieu R. Bloch

Covert and secret quantum key distribution aims at generating information-theoretically secret bits between distant legitimate parties in a manner that remains provably undetectable by an adversary. We propose a framework in which to precisely define and analyze such an operation, and we show that c...


[Phys. Rev. A 99, 052329] Published Mon May 20, 2019

Categories: Journals, Physics

Gradient-based optimal control of open quantum systems using quantum trajectories and automatic differentiation

Mon, 2019-05-20 12:00

Author(s): Mohamed Abdelhafez, David I. Schuster, and Jens Koch

We present a gradient-based optimal-control technique for open quantum systems that utilizes quantum trajectories to simulate the quantum dynamics during optimization. Using trajectories allows for optimizing open systems with less computational cost than the regular density matrix approaches in mos...


[Phys. Rev. A 99, 052327] Published Mon May 20, 2019

Categories: Journals, Physics

Entanglement through qubit motion and the dynamical Casimir effect

Mon, 2019-05-20 12:00

Author(s): Andrés Agustí, Enrique Solano, and Carlos Sabín

We explore the interplay between acceleration radiation and the dynamical Casimir effect in the field of superconducting quantum technologies, analyzing the generation of entanglement between two qubits by means of the dynamical Casimir effect in several states of qubit motion. We show that the corr...


[Phys. Rev. A 99, 052328] Published Mon May 20, 2019

Categories: Journals, Physics

Efficient passive measurement-device-independent quantum key distribution

Fri, 2019-05-17 12:00

Author(s): Chun-Hui Zhang, Chun-Mei Zhang, and Qin Wang

To date, only active-decoy-state methods have been adopted in current measurement-device-independent (MDI) quantum key distribution (QKD) protocols, causing security loopholes when modulating multiple light intensities with practical devices. To solve this problem, the passive-decoy-state method wil...


[Phys. Rev. A 99, 052325] Published Fri May 17, 2019

Categories: Journals, Physics

Upper bounds on the quantum capacity for a general attenuator and amplifier

Fri, 2019-05-17 12:00

Author(s): Youngrong Lim, Soojoon Lee, Jaewan Kim, and Kabgyun Jeong

There have been several upper bounds on the quantum capacity of the single-mode Gaussian channels with thermal noise, such as thermal attenuator and amplifier. We consider a class of attenuator and amplifier with more general noises, including squeezing or even non-Gaussian noises. We derive upper b...


[Phys. Rev. A 99, 052326] Published Fri May 17, 2019

Categories: Journals, Physics

Decomposition of a symmetric multipartite observable

Thu, 2019-05-16 12:00

Author(s): You Zhou, Chenghao Guo, and Xiongfeng Ma

Production and verification of multipartite quantum state are an essential step in quantum information processing. In this work, we propose an efficient method to decompose symmetric multipartite observables, which are invariant under permutations between parties, with only (N+1)(N+2)/2 local measur...


[Phys. Rev. A 99, 052324] Published Thu May 16, 2019

Categories: Journals, Physics

Geometric formalism for constructing arbitrary single-qubit dynamically corrected gates

Wed, 2019-05-15 12:00

Author(s): Junkai Zeng, C. H. Yang, A. S. Dzurak, and Edwin Barnes

Implementing high-fidelity quantum control and reducing the effect of the coupling between a quantum system and its environment is a major challenge in developing quantum information technologies. Here, we show that there exists a geometrical structure hidden within the time-dependent Schrödinger eq...


[Phys. Rev. A 99, 052321] Published Wed May 15, 2019

Categories: Journals, Physics

Detection of out-of-time-order correlators and information scrambling in cold atoms: Ladder-$\mathit{XX}$ model

Wed, 2019-05-15 12:00

Author(s): Ceren B. Dağ and L.-M. Duan

Out-of-time-order correlators (OTOCs), recently at the center of discussion on quantum chaos, are tools to understand the information scrambling in different phases of quantum many-body systems. We propose a disordered ladder spin model, the XX ladder, which can be designed in a scalable cold atom s...


[Phys. Rev. A 99, 052322] Published Wed May 15, 2019

Categories: Journals, Physics

Statistical correlations between locally randomized measurements: A toolbox for probing entanglement in many-body quantum states

Wed, 2019-05-15 12:00

Author(s): A. Elben, B. Vermersch, C. F. Roos, and P. Zoller

We develop a general theoretical framework for measurement protocols employing statistical correlations of randomized measurements. We focus on locally randomized measurements implemented with local random unitaries in quantum lattice models. In particular, we discuss the theoretical details underly...


[Phys. Rev. A 99, 052323] Published Wed May 15, 2019

Categories: Journals, Physics