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The parameters of the quantum circuit in a variational quantum algorithm induce a landscape that contains the relevant information regarding its optimization hardness. In this work we investigate such landscapes through the lens of…

Quantum Physics · Physics 2024-03-05 Adrián Pérez-Salinas , Hao Wang , Xavier Bonet-Monroig

Variational quantum eigensolver (VQE) is demonstrated to be the promising methodology for quantum chemistry based on near-term quantum devices. However, many problems are yet to be investigated for this methodology, such as the influences…

Chemical Physics · Physics 2021-01-18 Xian-Hu Zha , Chao Zhang , Dengdong Fan , Pengxiang Xu , Shiyu Du , Rui-Qin Zhang , Chen Fu

Variational Quantum Algorithms (VQAs) are a class of hybrid quantum-classical algorithms that leverage on classical optimization tools to find the optimal parameters for a parameterized quantum circuit. One relevant application of VQAs is…

Quantum Physics · Physics 2026-01-26 Mirko Legnini , Julian Berberich

We characterize the early stages of the approach to equilibrium in isolated quantum systems through the evolution of the entanglement spectrum. We find that the entanglement spectrum of a subsystem evolves with at least three distinct…

Disordered Systems and Neural Networks · Physics 2019-11-12 Po-Yao Chang , Xiao Chen , Sarang Gopalakrishnan , J. H. Pixley

Correlations and measures of entanglement in ground state wavefunctions of relativistic quantum field theories are spatially localized over length scales set by the mass of the lightest particle. We utilize this localization to design…

Quantum Physics · Physics 2020-07-29 Natalie Klco , Martin J. Savage

An active area of investigation in the search for quantum advantage is Quantum Machine Learning. Quantum Machine Learning, and Parameterized Quantum Circuits in a hybrid quantum-classical setup in particular, could bring advancements in…

Quantum Physics · Physics 2020-09-01 Thomas Hubregtsen , Josef Pichlmeier , Patrick Stecher , Koen Bertels

The Variational Quantum Eigensolver (VQE) is a fundamental algorithm in quantum computing, yet a coherent geometric characterization of VQE remains missing due to fragmented analyses across fixed-ansatz and adaptive-circuit formulations. In…

Quantum Physics · Physics 2026-05-28 Zhen Qin

There has been great interest in recent years in quantum control landscapes. Given an objective $J$ that depends on a control field $\varepsilon$ the dynamical landscape is defined by the properties of the Hessian $\delta^2…

Quantum Physics · Physics 2015-08-25 Alexander N. Pechen , David J. Tannor

The entanglement spectrum of the reduced density matrix contains information beyond the von Neumann entropy and provides unique insights into exotic orders or critical behavior of quantum systems. Here, we show that strongly disordered…

Disordered Systems and Neural Networks · Physics 2016-10-14 Maksym Serbyn , Alexios A. Michailidis , Dmitry A. Abanin , Z. Papić

In various physical implementations of quantum information processing, qubits are realized in a Lambda type system configuration as two stable lower energy levels coupled indirectly via an unstable higher energy level, that is, in…

Quantum Physics · Physics 2025-11-11 Julia Cen , Domenico D'Alessandro

The reliable and precise generation of quantum unitary transformations is essential to the realization of a number of fundamental objectives, such as quantum control and quantum information processing. Prior work has explored the optimal…

Quantum Physics · Physics 2010-07-21 Michael Hsieh , Rebing Wu , Herschel Rabitz , Daniel Lidar

The control of quantum system dynamics is generally performed by seeking a suitable applied field. The physical objective as a functional of the field forms the quantum control landscape, whose topology, under certain conditions, has been…

Quantum Physics · Physics 2014-11-11 Arun Nanduri , Ofer M. Shir , Ashley Donovan , Tak-San Ho , Herschel Rabitz

Quantum-enhanced sensing promises to improve the performance of sensing tasks using non-classical probes and measurements that require far fewer scene-modulated photons than the best classical schemes, thereby granting…

Quantum Physics · Physics 2021-08-11 Michael R. Grace , Christos N. Gagatsos , Saikat Guha

Quantum processing units boost entanglement at the level of hardware and enable physical simulations of highly correlated electron states in molecules and intermolecular chemical bonds. The variational quantum eigensolver provides a…

For quantum annealing, as opposed to circuit based quantum computing, the solution to a computational problem is encoded in the ground state of a quantum system. Therefore its susceptibility to environmental effects is a different but not…

Quantum Physics · Physics 2018-09-25 Tobias Chasseur , Stefan Kehrein , Frank K. Wilhelm

Variational quantum algorithms (VQAs) combining the advantages of parameterized quantum circuits and classical optimizers, promise practical quantum applications in the Noisy Intermediate-Scale Quantum era. The performance of VQAs heavily…

Entanglement is the crucial ingredient of quantum many-body physics, and characterizing and quantifying entanglement in closed system dynamics of quantum simulators is an outstanding challenge in today's era of intermediate scale quantum…

Quantum Physics · Physics 2021-08-31 Christian Kokail , Rick van Bijnen , Andreas Elben , Benoît Vermersch , Peter Zoller

Variational quantum algorithms (VQAs) have emerged as the leading strategy to obtain quantum advantage on the current noisy intermediate-scale devices. However, their entanglement-trainability correlation, as the major reason for the barren…

Quantum Physics · Physics 2025-05-07 Shikun Zhang , Yang Zhou , Zheng Qin , Rui Li , Chunxiao Du , Zhisong Xiao , Yongyou Zhang

Parameterized quantum circuits play an essential role in the performance of many variational hybrid quantum-classical (HQC) algorithms. One challenge in implementing such algorithms is to choose an effective circuit that well represents the…

Quantum Physics · Physics 2020-01-15 Sukin Sim , Peter D. Johnson , Alan Aspuru-Guzik

The quantum fisher information and quantum correlation parameters are employed to study the application of non-classical light to the problem of parameter estimation. It is shown that the optimal measurement sensitivity of a quantum state…

Quantum Physics · Physics 2015-01-09 Jaspreet Sahota , Nicolás Quesada