QUROPE Quantum Information Processing and Communication in Europe

Author(s): Mattheus Burkhard, Onur Pusuluk, and Tristan Farrow

The resource theory of quantum thermodynamics has emerged as a powerful tool for exploring the out-of-equilibrium dynamics of microscopic and highly correlated systems. Recently, it has been employed in photoisomerization, a mechanism facilitating vision through the isomerism of the photoreceptor pr…

[Phys. Rev. A 110, 012411] Published Mon Jul 01, 2024

Author(s): Xinyu Qiu, Lin Chen, and Li-Jun Zhao

Quantifying the effect of noise on unitary operations is an essential task in quantum information processing. We propose the quantum Wasserstein distance between unitary operations, which shows an explanation for quantum circuit complexity and characterizes the local distinguishability of multiqudit…

[Phys. Rev. A 110, 012412] Published Mon Jul 01, 2024

Author(s): Hao Sun, Fenzhuo Guo, Haifeng Dong, and Fei Gao

Quantum network nonlocality sharing provides a unique perspective for constructing large-scale quantum networks and holds promise for numerous potential applications. In this paper we demonstrate the network nonlocality sharing via unsharp measurements in a two-forked n-layer tree-shaped network, wh…

[Phys. Rev. A 110, 012401] Published Mon Jul 01, 2024

Author(s): Ran Liu, Xiaodong Yang, and Jun Li

Resisting diverse noise effects is crucial for the accurate manipulation of quantum systems. For static or slowly varying noises, many efficient noise mitigation strategies have been developed, such as composite pulses and dynamical decoupling. However, for fast fluctuating noise in the Markovian li…

[Phys. Rev. A 110, 012402] Published Mon Jul 01, 2024

Author(s): Maciej Demianowicz, Kajetan Vogtt, and Remigiusz Augusiak

We introduce a class of entangled subspaces: completely entangled subspaces of entanglement depth k (k−CESs). These are subspaces of multipartite Hilbert spaces containing only pure states with an entanglement depth of at least k. We present an efficient construction of k−CESs of any achievable dime…

[Phys. Rev. A 110, 012403] Published Mon Jul 01, 2024

Author(s): Alexey Uvarov, Daniil Rabinovich, Olga Lakhmanskaya, Kirill Lakhmanskiy, Jacob Biamonte, and Soumik Adhikary

Variational quantum algorithms have emerged as a cornerstone of contemporary quantum algorithms research. Practical implementations of these algorithms, despite offering certain levels of robustness against systematic errors, show a decline in performance due to the presence of stochastic errors and…

[Phys. Rev. A 110, 012404] Published Mon Jul 01, 2024

Author(s): Yu Guo

Multipartite entanglement includes not only the genuine entanglement but also the k-entanglement (k⩾2). It is known that the most bipartite entanglement measures have been shown to be monogamous, but the monogamy relation is involved in the bipartite entanglement measures rather than the multipartit…

[Phys. Rev. A 110, 012405] Published Mon Jul 01, 2024

Author(s): Si-Yuan Qi, Geni Gupur, Yu-Chun Wu, and Guo-Ping Guo

Equivalence between positive partial transpose (PPT) entanglement and bound entanglement is a long-standing open problem in quantum information theory. Limited progress has been made so far, even on the seemingly simple case of the bound entanglement of Werner states. The primary challenge is to giv…

[Phys. Rev. A 110, 012406] Published Mon Jul 01, 2024

Author(s): Paweł Cieśliński, Paweł Kurzyński, Tomasz Sowiński, Waldemar Kłobus, and Wiesław Laskowski

The investigation of many-body interactions holds significant importance for both quantum foundations and information. Hamiltonians coupling multiple particles at once, beyond other applications, can lead to faster entanglement generation, multiqubit gate implementation, and improved error correctio…

[Phys. Rev. A 110, 012407] Published Mon Jul 01, 2024

Author(s): Anaelle Hertz, Aaron Z. Goldberg, and Khabat Heshami

The quadrature coherence scale (QCS) is a recently introduced measure that was shown to be an efficient witness of nonclassicality. It takes a simple form for pure and Gaussian states, but a general expression for mixed states tends to be prohibitively unwieldy. In this paper we introduce a method f…

[Phys. Rev. A 110, 012408] Published Mon Jul 01, 2024

Author(s): Yudai Suzuki and Muyuan Li

Quantum kernel methods have been actively examined from both theoretical and practical perspectives due to the potential of quantum advantage in machine learning tasks. Despite a provable advantage of fine-tuned quantum kernels for specific problems, widespread practical usage of quantum kernel meth…

[Phys. Rev. A 110, 012409] Published Mon Jul 01, 2024

Author(s): Sudipta Das, Rivu Gupta, Himadri Shekhar Dhar, and Aditi Sen(De)

The telecloning protocol distributes quantum states from a single sender to multiple receivers via a shared entangled state by exploiting the notions of teleportation and approximate cloning. We investigate the optimal telecloning fidelities obtained using both Gaussian and non-Gaussian shared resou…

[Phys. Rev. A 110, 012410] Published Mon Jul 01, 2024

Author(s): Paulo J. Paulino, Igor Lesanovsky, and Federico Carollo

The state of an open quantum system undergoing an adiabatic process evolves by following the instantaneous stationary state of its time-dependent generator. This observation allows one to characterize, for a generic adiabatic evolution, the average dynamics of the open system. However, information a…

[Phys. Rev. Lett. 132, 260402] Published Fri Jun 28, 2024

Author(s): Marcin Łobejko, Tanmoy Biswas, Paweł Mazurek, and Michał Horodecki

We demonstrate how to incorporate a catalyst to enhance the performance of a heat engine. Specifically, we analyze efficiency in one of the simplest engine models, which operates in only two strokes and comprises of a pair of two-level systems, potentially assisted by a d-dimensional catalyst. When …

[Phys. Rev. Lett. 132, 260403] Published Fri Jun 28, 2024

Author(s): Jiu-Peng Chen, Fei Zhou, Chi Zhang, Cong Jiang, Fa-Xi Chen, Jia Huang, Hao Li, Li-Xing You, Xiang-Bin Wang, Yang Liu, Qiang Zhang, and Jian-Wei Pan

Twin-field quantum key distribution (TFQKD) overcomes the linear rate-loss limit, which promises a boost of secure key rate over long distance. However, the complexity of eliminating the frequency differences between the independent laser sources hinders its practical application. We analyzed and de…

[Phys. Rev. Lett. 132, 260802] Published Fri Jun 28, 2024

Author(s): Mark Buchanan

A theoretical model for the illumination of photosynthesizing algae in giant clams suggests principles for high efficiency collection of sunlight.

[Physics 17, 106] Published Fri Jun 28, 2024

The Ozawa's Intersubjectivity Theorem (OIT) proved within quantum measurement theory supports the new postulate of relational quantum mechanics (RQM), the postulate on internally consistent descriptions. But from OIT viewpoint postulate's formulation should be completed by the assumption of probability reproducibility

The frontier of quantum computing (QC) simulation on classical hardware is quickly reaching the hard scalability limits for computational feasibility. Nonetheless, there is still a need to simulate large quantum systems classically, as the Noisy Intermediate Scale Quantum (NISQ) devices are yet to be considered fault tolerant and performant enough in terms of operations per second. Each of the two main exact simulation techniques, state vector and tensor network simulators, boasts specific limitations. The exponential memory requirement of state vector simulation, when compared to the qubit register sizes of currently available quantum computers, quickly saturates the capacity of the top HPC machines currently available. Tensor network contraction approaches, which encode quantum circuits into tensor networks and then contract them over an output bit string to obtain its probability amplitude, still fall short of the inherent complexity of finding an optimal contraction path, which maps to a max-cut problem on a dense mesh, a notably NP-hard problem.

This article aims at investigating the limits of current state-of-the-art simulation techniques on a test bench made of eight widely used quantum subroutines, each in 31 different configurations, with special emphasis on performance. We then correlate the performance measures of the simulators with the metrics that characterise the benchmark circuits, identifying the main reasons behind the observed performance trend. From our observations, given the structure of a quantum circuit and the number of qubits, we highlight how to select the best simulation strategy, obtaining a speedup of up to an order of magnitude.

We show how a driven-dissipative cavity coupled to a collective ensemble of atoms can dynamically generate metrologically useful spin-squeezed states. In contrast to other dissipative approaches, we do not rely on complex engineered dissipation or input states, nor do we require tuning the system to a critical point. Instead, we utilize a strong symmetry, a special type of symmetry that can occur in open quantum systems and emerges naturally in systems with collective dissipation, such as superradiance. This symmetry preserves coherence and allows for the accumulation of an atom number-dependent Berry phase which in turn creates spin-squeezed states via emergent one-axis twisting dynamics. This work shows that it is possible to generate entanglement in an atom-cavity resonant regime with macroscopic optical excitations of the system, going beyond the typical dispersive regime with negligible optical excitations often utilized in current cavity QED experiments.

Dissipative processes can drive different magnetic orders in quantum spin chains. Using a non-perturbative analytic mapping framework, we systematically show how to structure different magnetic orders in spin systems by controlling the locality of the attached baths. Our mapping approach reveals analytically the impact of spin-bath couplings, leading to the suppression of spin splittings, bath-dressing and mixing of spin-spin interactions, and emergence of non-local ferromagnetic interactions between spins coupled to the same bath, which become long-ranged for a global bath. Our general mapping method can be readily applied to a variety of spin models: We demonstrate (i) a bath-induced transition from antiferromangnetic (AFM) to ferromagnetic ordering in a Heisenberg spin chain, (ii) AFM to extended Neel phase ordering within a transverse-field Ising chain with pairwise couplings to baths, and (iii) a quantum phase transition in the fully-connected Ising model. Our method is non-perturbative in the system-bath coupling. It holds for a variety of non-Markovian baths and it can be readily applied towards studying bath-engineered phases in frustrated or topological materials.