QUROPE Quantum Information Processing and Communication in Europe

Author(s): Sarah Brandsen, Mengke Lian, Kevin D. Stubbs, Narayanan Rengaswamy, and Henry D. Pfister

Discriminating between quantum states is a fundamental task in quantum information theory. Given two quantum states ρ+ and ρ−, the Helstrom measurement distinguishes between them with minimal probability of error. However, finding and experimentally implementing the Helstrom measurement can be chall…

[Phys. Rev. A 106, 012408] Published Wed Jul 06, 2022

Author(s): Dominik Koutný, Libor Motka, Zdeněk Hradil, Jaroslav Řeháček, and Luis L. Sánchez-Soto

We revisit the application of neural networks to quantum state tomography. We confirm that the positivity constraint can be successfully implemented with trained networks that convert outputs from standard feed-forward neural networks to valid descriptions of quantum states. Any standard neural-netw…

[Phys. Rev. A 106, 012409] Published Wed Jul 06, 2022

Author(s): Andreas Ketterer, Satoya Imai, Nikolai Wyderka, and Otfried Gühne

We consider statistical methods based on finite samples of locally randomized measurements in order to certify different degrees of multiparticle entanglement in intermediate-scale quantum systems. We first introduce hierarchies of multiqubit criteria, satisfied by states which are separable with re…

[Phys. Rev. A 106, L010402] Published Wed Jul 06, 2022

Author(s): Anton N. Vetlugin, Ruixiang Guo, Cesare Soci, and Nikolay I. Zheludev

Advanced quantum information protocols rely on the operation of multinodal quantum networks where entanglement is distributed across the nodes. Existing protocols of entanglement generation are probabilistic, with the efficiency dropping exponentially with the size of the system. We formulate an app…

[Phys. Rev. A 106, 012402] Published Tue Jul 05, 2022

Author(s): Kazuki Akimoto, Shunji Tsuchiya, Ryosuke Yoshii, and Yuki Takeuchi

Graph states are entangled resource states for universal measurement-based quantum computation. Although matter qubits such as superconducting circuits and trapped ions are promising candidates to generate graph states, it is technologically hard to entangle a large number of them due to several typ…

[Phys. Rev. A 106, 012405] Published Tue Jul 05, 2022

Author(s): Diego Paiva Pires

We discuss a class of quantum speed limits (QSLs) based on unified quantum (α,μ)-entropy for nonunitary physical processes. The bounds depend on both the Schatten speed and the smallest eigenvalue of the evolved state and the two-parametric unified entropy. We specialize these results to quantum cha…

[Phys. Rev. A 106, 012403] Published Tue Jul 05, 2022

Author(s): Boyu Zhou, Anthony J. Brady, and Quntao Zhuang

Entanglement has shown promise in enhancing information processing tasks in a sensor network via distributed quantum sensing protocols. As noise is ubiquitous in sensor networks, error correction schemes based on Gottesman-Kitaev-Preskill (GKP) states are required to enhance the performance, as show…

[Phys. Rev. A 106, 012404] Published Tue Jul 05, 2022

Author(s): Meng-Han Chen, Chao-Hua Yu, Jian-Liang Gao, Kai Yu, Song Lin, Gong-De Guo, and Jing Li

The Gaussian process is a widely used model for regression problems in supervised machine learning. However, predicting new inputs via a Gaussian process model becomes computationally inefficient when training a large data set. This paper proposes a fast quantum algorithm for prediction based on the…

[Phys. Rev. A 106, 012406] Published Tue Jul 05, 2022

Author(s): F. Hahn, A. Dahlberg, J. Eisert, and A. Pappa

Quantum communication research has in recent years shifted to include multipartite networks for which questions of quantum network routing naturally emerge. To understand the potential for multipartite routing, we focus on the most promising architectures for future quantum networks—those connecting…

[Phys. Rev. A 106, L010401] Published Tue Jul 05, 2022

Author(s): N. Gigena and J. Kaniewski

We introduce a three-parameter family of Bell functionals that extends those studied previously [Kaniewski, Phys. Rev. Res. 2, 033420 (2020)] by including a marginal contribution. An analysis of their largest value achievable by quantum realizations naturally splits the family into two branches, and…

[Phys. Rev. A 106, 012401] Published Fri Jul 01, 2022

Author(s): Madhura Ghosh Dastidar and Gniewomir Sarbicki

We consider a subgroup of unitary transformations on a mode of light induced by a Mach-Zehnder Interferometer and an algebra of observables describing a photon-number detector preceded by the interferometer. We explore the uncertainty principles between such observables and their usefulness in perfo…

[Phys. Rev. A 105, 062459] Published Thu Jun 30, 2022

Author(s): Yuan Sun, Nan Li, and Shunlong Luo

Quantum channels are indispensable instruments for transmitting, extracting, and processing information. According to the spirit of the Bohr complementarity principle and the Heisenberg uncertainty principle, one expects that there are intrinsic tradeoff relations between state disturbance and infor…

[Phys. Rev. A 105, 062458] Published Wed Jun 29, 2022

Author(s): J. Agustí, Y. Minoguchi, J. M. Fink, and P. Rabl

We investigate the deterministic generation and distribution of entanglement in large quantum networks by driving distant qubits with the output fields of a nondegenerate parametric amplifier. In this setting, the amplifier produces a continuous Gaussian two-mode squeezed state, which acts as a quan…

[Phys. Rev. A 105, 062454] Published Wed Jun 29, 2022

Author(s): Jian Lin, Zhengfeng Zhang, Junping Zhang, and Xiaopeng Li

Prime factorization is a difficult problem with classical computing, whose exponential hardness is the foundation of Rivest-Shamir-Adleman cryptography. With programable quantum devices, adiabatic quantum computing has been proposed as a plausible approach to solve prime factorization, having promis…

[Phys. Rev. A 105, 062455] Published Wed Jun 29, 2022

Author(s): Jiahao Huang, Hongtao Huo, Min Zhuang, and Chaohong Lee

Spin cat states are promising candidates for achieving Heisenberg-limited quantum metrology. It is suggested that spin cat states can be generated by adiabatic evolution. However, due to the limited coherence time, the adiabatic process may be too slow to be practical. To speed up the state generati…

[Phys. Rev. A 105, 062456] Published Wed Jun 29, 2022

Author(s): Ryoji Miyazaki

A method of quantum annealing (QA) using Kerr-nonlinear parametric oscillators (KPOs) was proposed. This method is described by bosonic operators and has different characteristics from QA based on the transverse-field Ising model. As the first step to describe this method in the conventional framewo…

[Phys. Rev. A 105, 062457] Published Wed Jun 29, 2022

Author(s): Amit Saha, Ritajit Majumdar, Debasri Saha, Amlan Chakrabarti, and Susmita Sur-Kolay

The progress in building quantum computers to execute quantum algorithms has recently been remarkable. Grover's search algorithm in a binary quantum system provides a considerable speed-up over the classical paradigm. It can be extended to a d-ary (qudit) quantum system also for utilizing the advant…

[Phys. Rev. A 105, 062453] Published Tue Jun 28, 2022

Author(s): Xinyu Qiu and Lin Chen

Quantum cost is a key ingredient in evaluating the quality of quantum protocols from a practical viewpoint. We show that the quantum cost of a d-dimensional dense coding protocol is equal to d+3 when transmitting the classical message (0,0) and d+4 when transmitting another classical message. It app…

[Phys. Rev. A 105, 062451] Published Mon Jun 27, 2022

Author(s): Oliver Hahn, Patric Holmvall, Pascal Stadler, Giulia Ferrini, and Alessandro Ferraro

In the context of quantum technologies over continuous variables, Gaussian states and operations are typically regarded as freely available, as they are relatively easily accessible experimentally. In contrast, the generation of non-Gaussian states, as well as the implementation of non-Gaussian oper…

[Phys. Rev. A 105, 062446] Published Mon Jun 27, 2022

Author(s): Hector Spencer-Wood, John Jeffers, and Sarah Croke

We consider measurement disturbance tradeoffs in quantum machine learning protocols which seek to learn about quantum data. We study the simplest example of a binary classification task in the unsupervised regime. Specifically, we investigate how a classification of two qubits, that can each be in o…

[Phys. Rev. A 105, 062447] Published Mon Jun 27, 2022