QUROPE Quantum Information Processing and Communication in Europe

Author(s): Moein Naseri, Tulja Varun Kondra, Suchetana Goswami, Marco Fellous-Asiani, and Alexander Streltsov

Quantum algorithms can outperform their classical counterparts in various tasks, the most prominent example being Shor's algorithm for efficient prime factorization on a quantum computer. It is clear that one of the reasons for the speedup is the superposition principle of quantum mechanics, which a…

[Phys. Rev. A 106, 062429] Published Wed Dec 21, 2022

Author(s): Antonio deMarti iOlius, Josu Etxezarreta Martinez, Patricio Fuentes, Pedro M. Crespo, and Javier Garcia-Frias

Surface codes are generally studied based on the assumption that each of the qubits that make up the surface code lattice suffers noise that is independent and identically distributed (i.i.d.). However, real benchmarks of the individual relaxation (T1) and dephasing (T2) times of the constituent qub…

[Phys. Rev. A 106, 062428] Published Wed Dec 21, 2022

Author(s): Florian Meier and Lídia del Rio

We consider two bottlenecks in quantum computing: limited memory size and noise caused by heat dissipation. Trying to optimize both, we investigate “on-the-go erasure” of quantum registers that are no longer needed for a given algorithm: freeing up auxiliary qubits as they stop being useful would fa…

[Phys. Rev. A 106, 062426] Published Tue Dec 20, 2022

Author(s): Zahra Raissi, Adam Burchardt, and Edwin Barnes

Highly entangled multipartite states such as k-uniform (k-UNI) and absolutely maximally entangled (AME) states serve as critical resources in quantum networking and other quantum information applications. However, there does not yet exist a complete classification of such states, and much remains un…

[Phys. Rev. A 106, 062424] Published Mon Dec 19, 2022

Author(s): Markus Frembs and Andreas Döring

Characterizing quantum correlations from physical principles is a central problem in the field of quantum information theory. Entanglement breaks bounds on correlations put forth by Bell's theorem, thus challenging the notion of local causality as a physical principle. A natural relaxation is to stu…

[Phys. Rev. A 106, 062420] Published Mon Dec 19, 2022

Author(s): Mordecai Waegell and P. K. Aravind

It is shown that the codewords of the binary and ternary Golay codes can be converted into rays in RP23 and RP11 that provide proofs of the Kochen-Specker theorem in real state spaces of dimensions 24 and 12, respectively. Some implications of these results are discussed.

[Phys. Rev. A 106, 062421] Published Mon Dec 19, 2022

Author(s): Ming Yuan, Qian Xu, and Liang Jiang

Fault-tolerant quantum computation with depolarization error often requires demanding error threshold and resource overhead. If the operations can maintain high noise bias—dominated by dephasing error with small bit-flip error—we can achieve hardware-efficient fault-tolerant quantum computation with…

[Phys. Rev. A 106, 062422] Published Mon Dec 19, 2022

Author(s): Jack Y. Araz and Michael Spannowsky

Tensor networks (TN) are approximations of high-dimensional tensors designed to represent locally entangled quantum many-body systems efficiently. This paper provides a comprehensive comparison between classical TNs and TN-inspired quantum circuits in the context of machine learning on highly comple…

[Phys. Rev. A 106, 062423] Published Mon Dec 19, 2022

Author(s): Mohammad Ali Javidian, Vaneet Aggarwal, and Zubin Jacob

Quantum causality is an emerging field of study which has the potential to greatly advance our understanding of quantum systems. In this paper, we put forth a theoretical framework for merging quantum information science and causal inference by exploiting entropic principles. For this purpose, we le…

[Phys. Rev. A 106, 062425] Published Mon Dec 19, 2022

Author(s): Antonio A. Mele, Glen B. Mbeng, Giuseppe E. Santoro, Mario Collura, and Pietro Torta

Parametrized quantum circuits inspired by adiabatic quantum computation often suffer from vanishing gradients, hindering the trainability of hybrid quantum-classical algorithms. Here, the authors put forward a strategy to overcome this by reusing parameters and iterating from small to large systems.

[Phys. Rev. A 106, L060401] Published Mon Dec 19, 2022

Author(s): Cynthia Keeler, William Munizzi, and Jason Pollack

The n-qubit stabilizer states are those left invariant by a 2n-element subset of the Pauli group. The Clifford group is the group of unitaries which take stabilizer states to stabilizer states; a physically motivated generating set, the Hadamard, phase, and controlled-not (cnot) gates which comprise…

[Phys. Rev. A 106, 062418] Published Fri Dec 16, 2022

Author(s): Duarte Magano and Miguel Murça

The problem of phase estimation (or amplitude estimation) admits a quadratic quantum speedup. Wang, Higgott, and Brierley [Wang, Higgott, and Brierley, Phys. Rev. Lett. 122, 140504 (2019)] have shown that there is a continuous tradeoff between quantum speedup and circuit depth [by defining a family …

[Phys. Rev. A 106, 062419] Published Fri Dec 16, 2022

Author(s): Nicole Yunger Halpern, Naga B. T. Kothakonda, Jonas Haferkamp, Anthony Munson, Jens Eisert, and Philippe Faist

Quantum complexity is emerging as a key property of many-body systems, including black holes, topological materials, and early quantum computers. A state's complexity quantifies the number of computational gates required to prepare the state from a simple tensor product. The greater a state's distan…

[Phys. Rev. A 106, 062417] Published Thu Dec 15, 2022

Author(s): Llorenç Escolà-Farràs and Daniel Braun

We extend Pearl's definition of causal influence to the quantum domain, where two quantum systems A, B with finite-dimensional Hilbert space are embedded in a common environment C and propagated with a joint unitary U. For a finite-dimensional Hilbert space C, we find the necessary and sufficient co…

[Phys. Rev. A 106, 062415] Published Wed Dec 14, 2022

Author(s): Bálint Koczor and Simon C. Benjamin

Variational quantum algorithms are promising tools whose efficacy depends on their optimization method. For noise-free unitary circuits, the quantum generalization of natural gradient descent has been introduced and shown to be equivalent to imaginary time evolution: the approach is effective due to…

[Phys. Rev. A 106, 062416] Published Wed Dec 14, 2022

Author(s): Alicia B. Magann, Kenneth M. Rudinger, Matthew D. Grace, and Mohan Sarovar

The prospect of using quantum computers to solve combinatorial optimization problems via the quantum approximate optimization algorithm (QAOA) has attracted considerable interest in recent years. However, a key limitation associated with QAOA is the need to classically optimize over a set of quantum…

[Phys. Rev. A 106, 062414] Published Tue Dec 13, 2022

Author(s): Mirko Consiglio, Tony J. G. Apollaro, and Marcin Wieśniak

We present the variational separability verifier (VSV), which is a variational quantum algorithm that determines the closest separable state (CSS) of an arbitrary quantum state with respect to the Hilbert-Schmidt distance (HSD). We first assess the performance of the VSV by investigating the converg…

[Phys. Rev. A 106, 062413] Published Tue Dec 13, 2022

Author(s): R. A. Ribeiro, A. A. Matoso, L. E. Oxman, A. Z. Khoury, and S. Pádua

We observe experimentally the fractional topological phase (FTP) robustness to the dephasing noise in two-qudit photonic systems. We use a source of photon pairs generated by spontaneous parametric down-conversion, hyperentangled in the polarization and photon path degrees of freedom. The dephasing …

[Phys. Rev. A 106, 062411] Published Mon Dec 12, 2022

Author(s): Xiao-Xu Zhang, Mu-Sheng Jiang, Yang Wang, Yi-Fei Lu, Hong-Wei Li, Chun Zhou, Yu Zhou, and Wan-Su Bao

Many security loopholes exist in quantum key distribution (QKD) due to the imperfections of realistic devices. On the source side, the decoy-state method can defend against the most severe photon-number-splitting (PNS) attack and improve the performance of QKD. Measurement-device-independent QKD and…

[Phys. Rev. A 106, 062412] Published Mon Dec 12, 2022

Author(s): Viktor Nordgren, Olga Leskovjanová, Jan Provazník, Adam Johnston, Natalia Korolkova, and Ladislav Mišta, Jr.

Genuine multipartite entanglement underlies correlation experiments corroborating quantum mechanics and it is an expedient empowering many quantum technologies. One of many counterintuitive facets of genuine multipartite entanglement is its ability to exhibit an emergent character. That is, one can …

[Phys. Rev. A 106, 062410] Published Fri Dec 09, 2022