QUROPE Quantum Information Processing and Communication in Europe

Author(s): Bao-Jie Liu, Ying-Ying Wang, Tal Sheffer, and Chen Wang

We report observations of discrete charge states of a coherent two-level system (TLS) that is strongly coupled to an offset-charge-sensitive superconducting transmon qubit. We measure an offset charge of 0.072e associated with the two TLS eigenstates, which have a transition frequency of 2.9 GHz and…

[Phys. Rev. Lett. 133, 160602] Published Thu Oct 17, 2024

Author(s): Chang-Kang Hu, Chao Wei, Chilong Liu, Liangyu Che, Yuxuan Zhou, Guixu Xie, Haiyang Qin, Guantian Hu, Haolan Yuan, Ruiyang Zhou, Song Liu, Dian Tan, Tao Xin, and Dapeng Yu

Quantum state tomography (QST) via local measurements on reduced density matrices (LQST) is a promising approach but becomes impractical for large systems. To tackle this challenge, we developed an efficient quantum state tomography method inspired by quantum overlapping tomography [Phys. Rev. Lett.…

[Phys. Rev. Lett. 133, 160801] Published Thu Oct 17, 2024

Author(s): Jacob S. Nelson and Andrew D. Baczewski

We compare several quantum phase estimation (QPE) protocols intended for early fault-tolerant (EFT) quantum computers in the context of models of their implementations on a surface code architecture. We estimate the logical and physical resources required to use these protocols to calculate the grou…

[Phys. Rev. A 110, 042420] Published Wed Oct 16, 2024

Author(s): Lu Wang, Shu-Qian Liu, Feng-lin Wu, Hao Fan, and Si-Yuan Liu

We investigate the performances of multiphoton anisotropic Dicke quantum battery (QB), which couples a finite number N of identical and independent two-level systems (TLSs) to a unique cavity mode. Each transition of TLS is accompanied by the absorption or emission of l photons from the cavity mode.…

[Phys. Rev. A 110, 042419] Published Wed Oct 16, 2024

Author(s): Arnab Adhikary, Wang Yang, and Robert Raussendorf

Quantum states picked from nontrivial symmetry-protected topological (SPT) phases have computational power in measurement-based quantum computation. This power is uniform across SPT phases, and is unlocked by measurements that break the symmetry. Except at special points in the phase, all computatio…

[Phys. Rev. Lett. 133, 160601] Published Wed Oct 16, 2024

Author(s): Ugo Nzongani, Nathanaël Eon, Iván Márquez-Martín, Armando Pérez, Giuseppe Di Molfetta, and Pablo Arrighi

Discrete-time quantum walks (QWs) are transportation models of single quantum particles over a lattice. Their evolution is driven through causal and local unitary operators. QWs are a powerful tool for quantum simulation of fundamental physics, as some of them have a continuum limit converging to we…

[Phys. Rev. A 110, 042418] Published Wed Oct 16, 2024

Author(s): A. D. Leu, M. C. Smith, M. F. Gely, and D. M. Lucas

This work presents a hybrid optical-microwave state preparation scheme for trapped ions with nuclear spin I > 1/2 at intermediate magnetic fields. This method provides a robust solution for high-fidelity state preparation that eliminates the need for polarization purity, making it well suited for scalable quantum computing systems.

[Phys. Rev. A 110, L040402] Published Wed Oct 16, 2024

Author(s): Jayameenakshi Venkatraman, Xu Xiao, Rodrigo G. Cortiñas, and Michel H. Devoret

Out-of-equilibrium driven nonlinear oscillators have attracted interest as a platform for tailoring Floquet Hamiltonian spectra and stabilizing quantum states for quantum information. However, it is usually ignored that the necessary parametric drive can amplify environmental fluctuations limiting a…

[Phys. Rev. A 110, 042411] Published Tue Oct 15, 2024

Author(s): Yi-Jun Luo, Xuan Leng, and Chengjie Zhang

In recent years, the detection of genuine multipartite entanglement (GME) via machine learning has received scant attention. Here, we employ convolutional neural networks (CNNs), as well as CNNs enhanced with squeeze and excitation (SE) to detect GME. We randomly generated GME states with 4 to 6 qub…

[Phys. Rev. A 110, 042412] Published Tue Oct 15, 2024

Author(s): Kang-Kang Yang, Zhi-Xi Wang, and Shao-Ming Fei

The concept of wave-particle duality holds significant importance in the field of quantum mechanics, as it elucidates the dual nature encompassing both wavelike and particlelike properties exhibited by microscopic particles. In this paper, we construct generalized measures for the predictability and…

[Phys. Rev. A 110, 042413] Published Tue Oct 15, 2024

Author(s): Zhen-Qiu Zhong, Xiao-Hai Zhan, Shuang Wang, Zhen-Qiang Yin, De-Yong He, Wei Chen, Guang-Can Guo, and Zheng-Fu Han

Time-bin entanglement is a critical resource in quantum information science owing to its exceptional robustness over long-distance channels. Achieving high quantum interference visibility is indispensable for fundamental research and practical applications. To date, a model that can accurately descr…

[Phys. Rev. A 110, 042414] Published Tue Oct 15, 2024

Author(s): Francisco Guzman-Cajica and Francisco S. Guzmán

In this paper we use a variational quantum algorithm to solve initial value problems with the implicit Crank-Nicolson and the method of lines (MoL) evolution schemes. The unknown functions use a spectral decomposition with the Fourier basis. The examples developed to illustrate the implementation ar…

[Phys. Rev. A 110, 042415] Published Tue Oct 15, 2024

Author(s): Youssef Kora, Hadi Zadeh-Haghighi, Terrence C. Stewart, Khabat Heshami, and Christoph Simon

We study the performance of an Ising spin network for quantum reservoir computing in linear and nonlinear memory tasks. We investigate the extent to which quantumness enhances performance by monitoring the behavior of quantum entanglement, which we quantify by the partial transpose of the density ma…

[Phys. Rev. A 110, 042416] Published Tue Oct 15, 2024

Author(s): Jonas Duda and Thomas G. Wong

A quantum particle evolving by Schrödinger's equation in discrete space constitutes a continuous-time quantum walk on a graph of vertices and edges. When a vertex is marked by an oracle, the quantum walk effects a quantum search algorithm. Previous investigations of this quantum search algorithm on …

[Phys. Rev. A 110, 042417] Published Tue Oct 15, 2024

Author(s): Andreas Kell, Moritz Breyer, Daniel Eberz, and Michael Köhl

We study the Higgs mode of a strongly interacting Fermi gas in the crossover regime between a fermionic and bosonic superfluid. By periodically modulating the interaction strength of the gas, we parametrically excite the Higgs mode and study its resonance frequency and line width as a function of bo…

[Phys. Rev. Lett. 133, 150403] Published Fri Oct 11, 2024

Author(s): Volodymyr Sivak, Michael Newman, and Paul Klimov

Accurate decoding of quantum error-correcting codes is a crucial ingredient in protecting quantum information from decoherence. It requires characterizing the error channels corrupting the logical quantum state and providing this information as a prior to the decoder. We introduce a reinforcement le…

[Phys. Rev. Lett. 133, 150603] Published Fri Oct 11, 2024

Author(s): Antonio Francesco Mello, Alessandro Santini, and Mario Collura

We introduce a novel hybrid approach combining tensor network methods with the stabilizer formalism to address the challenges of simulating many-body quantum systems. By integrating these techniques, we enhance our ability to accurately model unitary dynamics while mitigating the exponential growth …

[Phys. Rev. Lett. 133, 150604] Published Fri Oct 11, 2024

Author(s): Debarghya Chakraborty and Nikolaos Angelinos

We study the scaling of the ground-state entanglement entropy of various free fermionic models on one-dimensional lattices, where the hopping and pairing terms decay as a power law. We seek to understand the scaling of entanglement entropy in generic models as the exponent of the power law α is vari…

[Phys. Rev. A 110, 042408] Published Fri Oct 11, 2024

Author(s): Aakash Ravindra Shinde, Charu Jain, and Amir Kalev

Quantum convolutional neural network (QCNN), an early application for quantum computers in the noisy intermediate-scale quantum era, has been consistently proven successful as a machine learning (ML) algorithm for several tasks with significant accuracy. Derived from its classical counterpart, QCNN …

[Phys. Rev. A 110, 042409] Published Fri Oct 11, 2024

Author(s): Fabricio S. Lozano-Negro, Claudia M. Sánchez, Ana K. Chattah, Gonzalo A. Álvarez, and Horacio M. Pastawski

Out-of-time-order correlators (OTOCs) serve as a proxy for quantum information scrambling, which refers to the process where information stored locally disperses across the many-body degrees of freedom in a quantum system, rendering it inaccessible to local probes. Most experimental implementations …

[Phys. Rev. A 110, 042410] Published Fri Oct 11, 2024