QUROPE Quantum Information Processing and Communication in Europe

Author(s): Yating Ye and Xiao-Ming Lu

Recently a widely used computation expression for quantum Fisher information was shown to be discontinuous at the parameter points where the rank of the parametric density operator changes. The quantum Cramér-Rao bound can be violated on such singular parameter points if one uses this computation ex…

[Phys. Rev. A 106, 022429] Published Tue Aug 23, 2022

Author(s): Robert Barr, Yasuo Oda, Gregory Quiroz, B. David Clader, and Leigh M. Norris

We extend quantum noise spectroscopy (QNS) of amplitude control noise to settings where dephasing noise or detuning errors make significant contributions to qubit dynamics. Previous approaches to characterize amplitude noise are limited by their vulnerability to low-frequency dephasing noise and sta…

[Phys. Rev. A 106, 022425] Published Tue Aug 23, 2022

Author(s): Francesco Preti, Tommaso Calarco, Juan Mauricio Torres, and József Zsolt Bernád

We propose and investigate a method to optimize recurrence entanglement purification protocols. The approach is based on a numerical search in the whole set of SU(4) matrices with the aid of a quasi-Newton algorithm. Our method evaluates average concurrences where the probabilistic occurrence of mix…

[Phys. Rev. A 106, 022422] Published Mon Aug 22, 2022

Author(s): Sanaa Abaach, Mustapha Faqir, and Morad El Baz

The range of entanglement in quantum dots, under the effect of the Coulomb interaction and the system's size, is investigated. As ququart systems, naturally described by the Fermi-Hubbard model, we show that quantum dots supply long-range entanglement up to the third neighbor. In conjunction with th…

[Phys. Rev. A 106, 022421] Published Mon Aug 22, 2022

Author(s): Maxime Dupont, Nicolas Didier, Mark J. Hodson, Joel E. Moore, and Matthew J. Reagor

Many quantum algorithms seek to output a specific bitstring solving the problem of interest—or a few if the solution is degenerate. It is the case for the quantum approximate optimization algorithm (QAOA) in the limit of large circuit depth, which aims to solve quadratic unconstrained binary optimiz…

[Phys. Rev. A 106, 022423] Published Mon Aug 22, 2022

Author(s): Akshay Gaikwad, Arvind, and Kavita Dorai

We experimentally implement the Sz.-Nagy dilation algorithm to simulate open quantum dynamics on a nuclear magnetic resonance quantum processor. The Sz.-Nagy algorithm enables the simulation of the dynamics of an n-qubit system using n+1 qubits. We experimentally simulate the action of three nonunit…

[Phys. Rev. A 106, 022424] Published Mon Aug 22, 2022

Author(s): Peter Høyer and Janet Leahy

The defining feature of memoryless quantum walks is that they operate on the vertex space of a graph and therefore can be used to produce search algorithms with minimal memory. We present a memoryless walk that can find a unique marked vertex on a two-dimensional lattice. Our walk is based on the co…

[Phys. Rev. A 106, 022418] Published Fri Aug 19, 2022

Author(s): Guo Xuan Chan and Xin Wang

Long-range interaction between distant spins is an important building block for the realization of a large quantum-dot network in which couplings between pairs of spins can be selectively addressed. Recent experiments on the coherent oscillation of logical states between remote spins facilitated by …

[Phys. Rev. A 106, 022420] Published Fri Aug 19, 2022

Author(s): Lijun Huang, Zhi Tan, Honghua Zhong, and Bo Zhu

We propose a fast, robust, and long-distance quantum state transfer (QST) protocol via a splicing Su-Schrieffer-Heeger (SSH) chain, where the interchain couplings vary with the change in the phase parameter and the single or splicing SSH chain can be designed by adjusting it. It is found that the ex…

[Phys. Rev. A 106, 022419] Published Fri Aug 19, 2022

Author(s): G. J. Delben, A. L. O. dos Santos, and M. G. E. da Luz

We investigate the quantum control of two qubits interacting with a Markovian environment and evolving as an X state. The control is implemented via a simple applied field, whose profile is determined by means of the piecewise time-independent quantum control method. The goal is to make either the p…

[Phys. Rev. A 106, 022417] Published Fri Aug 19, 2022

Author(s): Fattah Sakuldee, Philip Taranto, and Simon Milz

Understanding the demarcation line between classical and quantum is an important issue in modern physics. The development of such an understanding requires a clear picture of the various concurrent notions of “classicality” in quantum theory presently in use. Here we focus on the relationship betwee…

[Phys. Rev. A 106, 022416] Published Thu Aug 18, 2022

Author(s): Marcel Seelbach Benkner, Jens Siewert, Otfried Gühne, and Gael Sentís

We introduce a family of highly symmetric bipartite quantum states in arbitrary dimensions. It consists of all states that are invariant under local phase rotations and local cyclic permutations of the basis. We solve the separability problem for a subspace of these states and show that a sizable pa…

[Phys. Rev. A 106, 022415] Published Wed Aug 17, 2022

Author(s): Anthony W. Schlimgen, Kade Head-Marsden, LeeAnn M. Sager-Smith, Prineha Narang, and David A. Mazziotti

Realizing nonunitary transformations on unitary-gate-based quantum devices is critically important for simulating a variety of physical problems, including open quantum systems and subnormalized quantum states. We present a dilation-based algorithm to simulate nonunitary operations using probabilist…

[Phys. Rev. A 106, 022414] Published Tue Aug 16, 2022

Author(s): X. N. Feng, Jiahao Huang, L. F. Wei, and Chaohong Lee

Inspired by the recent work [Nature (London) 521, 336 (2015)], we propose a scheme to suppress the backaction-induced dephasing of the spin state in a spin-oscillator system by squeezing the quantum fluctuation of the two-mode oscillator. We show specifically that squeezing either on a single mode i…

[Phys. Rev. A 106, 022413] Published Tue Aug 16, 2022

Author(s): Chu Guo

For a quantum system undergoing non-Markovian open quantum dynamics, we demonstrate a tomography algorithm based on multitime measurements of the system, which reconstructs a minimal environment coupled to the system, such that the system plus environment undergoes unitary evolution and that the red…

[Phys. Rev. A 106, 022411] Published Mon Aug 15, 2022

Author(s): Xinxing Yuan, Yue Li, Mengxiang Zhang, Chang Liu, Mingdong Zhu, Xi Qin, Nikolay V. Vitanov, Yiheng Lin, and Jiangfeng Du

Quantum information processing with multilevel systems (qudits) provides additional features and applications than the two-level systems. However, qudits are more prone to dephasing and dynamical decoupling for qudits has never been experimentally demonstrated. Here, as a proof-of-principle demonstr…

[Phys. Rev. A 106, 022412] Published Mon Aug 15, 2022

Author(s): Simon Kiesewetter and Peter D. Drummond

We give a detailed theoretical derivation of the master equation for the coherent Ising machine. This is a quantum computational network with feedback, that approximately solves NP-hard combinatoric problems, including the traveling salesman problem and various extensions and analogs. There are two …

[Phys. Rev. A 106, 022409] Published Fri Aug 12, 2022

Author(s): Sahar Basiri-Esfahani and Farid Shahandeh

Theoretical and experimental studies have suggested the relevance of quantum coherence to the performance of photovoltaic and light-harvesting complex molecular systems. However, there are ambiguities regarding the validity of statements we can make about the coherence in such systems. Here, we anal…

[Phys. Rev. A 106, 022410] Published Fri Aug 12, 2022

Author(s): Marek Kopciuch and Szymon Pustelny

Reliable tomography of a quantum state of atoms in room-temperature vapors offers interesting applications in quantum-information science. To step toward the applications, here, we theoretical investigate a technique of reconstruction of a collective density matrix of atoms in a state of a total ang…

[Phys. Rev. A 106, 022406] Published Wed Aug 10, 2022

Author(s): Ismail Yunus Akhalwaya, Yang-Hui He, Lior Horesh, Vishnu Jejjala, William Kirby, Kugendran Naidoo, and Shashanka Ubaru

The boundary operator is a linear operator that acts on a collection of high-dimensional binary points (simplices) and maps them to their boundaries. This boundary map is one of the key components in numerous applications, including differential equations, machine learning, computational geometry, m…

[Phys. Rev. A 106, 022407] Published Wed Aug 10, 2022