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Causal reasoning is essential to science, yet quantum theory challenges it. Quantum correlations violating Bell inequalities defy satisfactory causal explanations within the framework of classical causal models. What is more, a theory…

Quantum Physics · Physics 2021-03-05 Jonathan Barrett , Robin Lorenz , Ognyan Oreshkov

Entanglement is a key resource of quantum science for tasks that require it to be shared among participants. Within atomic, condensed matter and photonic many-body systems the distribution and sharing of entanglement is of particular…

Quantum Physics · Physics 2015-11-16 Xiao-Feng Qian , Miguel A. Alonso , J. H. Eberly

Gate-based universal quantum computation is formulated in terms of two types of operations: local single-qubit gates, which are typically easily implementable, and two-qubit entangling gates, whose faithful implementation remains one of the…

Quantum Physics · Physics 2023-10-18 Xiaoqin Gao , Paul Appel , Nicolai Friis , Martin Ringbauer , Marcus Huber

Measurements profoundly impact quantum systems, and can be used to create novel states of matter out of equilibrium. We investigate the multipartite entanglement structure that emerges in hybrid quantum circuits involving unitaries and…

Quantum Physics · Physics 2025-07-04 Sebastien J Avakian , T. Pereg-Barnea , William Witczak-Krempa

We investigate the fundamental expressivity limits of quantum reservoir computing (QRC) by establishing a formal connection to parametrized quantum circuit quantum machine learning (PQC-QML). We analytically prove, and numerically…

This paper showed how a simple lumped parameter model of a circuit can yield correct quantum mechanical predictions of its behavior, even when there is quantum entanglement between components of that circuit. It addresses an important…

Quantum Physics · Physics 2017-12-21 Paul J. Werbos

Entanglement is a striking feature of quantum mechanics, and it has a key property called unextendibility. In this paper, we present a framework for quantifying and investigating the unextendibility of general bipartite quantum states.…

Quantum Physics · Physics 2024-03-28 Kun Wang , Xin Wang , Mark M. Wilde

Since the beginning of quantum mechanics, many puzzling phenomena which distinguish the quantum from the classical world, have appeared such as complementarity, entanglement or contextuality. All of these phenomena are based on the…

Quantum Physics · Physics 2016-11-24 S. Wölk

Quantum entanglement is known as a unique quantum feature that cannot be obtained by classical physics. Over the last several decades, however, such an understanding on quantum entanglement might have confined us in a limited world of weird…

Quantum Physics · Physics 2023-08-01 B. S. Ham

Quantum correlations are the singular, defining resource of quantum information science and metrology, forming the basis of every operational advantage that quantum systems hold over classical ones. Yet exact bounds on these…

Quantum Physics · Physics 2025-12-22 Samuel Alperin

We present a systematic study of how quantum circuit design, specifically the depth of the variational ansatz and the choice of quantum feature mapping, affects the performance of hybrid quantum-classical neural networks on a causal…

Quantum Physics · Physics 2026-02-10 Silvie Illésová , Tomasz Rybotycki , Piotr Gawron , Martin Beseda

I propose a novel interpretation of quantum theory, which I will call Environmental Determinacy-based (EnDQT). In contrast to the well-known interpretations of quantum theory, EnDQT has the benefit of not adding non-local,…

Quantum Physics · Physics 2024-08-06 Francisco Pipa

Over-parameterization is commonly used to increase the expressivity of variational quantum circuits (VQCs), yet deeper and more highly parameterized circuits often exhibit poor trainability and limited generalization. In this work, we…

Quantum Physics · Physics 2026-01-06 Jun Qi , Chao-Han Huck Yang , Pin-Yu Chen , Min-Hsiu Hsieh

The universality of quantum theory has been questioned ever since it was proposed. Key to this long-unsolved question is to test whether a given physical system has non-classical features. Here we connect recently proposed witnesses of…

The uncertainty principle and entanglement are two fundamental, but yet not well understood, features of quantum theory. The uncertainty relation reflects the capability limit in acquiring the knowledge of different physical properties of a…

Quantum Physics · Physics 2018-02-15 Jun-Li Li , Cong-Feng Qiao

Entanglement is the defining characteristic of quantum mechanics. Bipartite entanglement is characterized by the von Neumann entropy. Entanglement is not just described by a number, however; it is also characterized by its level of…

Quantum Physics · Physics 2022-09-26 Sarah True , Alioscia Hamma

The hybrid quantum-classical algorithm is actively examined as a technique applicable even to intermediate-scale quantum computers. To execute this algorithm, the hardware efficient ansatz is often used, thanks to its implementability and…

Quantum Physics · Physics 2021-04-21 Kouhei Nakaji , Naoki Yamamoto

One of the defining traits of quantum mechanics is the uncertainty principle which was originally expressed in terms of the standard deviation of two observables. Alternatively, it can be formulated using entropic measures, and can also be…

Quantum Physics · Physics 2015-09-30 Göktuğ Karpat , Jyrki Piilo , Sabrina Maniscalco

Discrete-time quantum walks provide a natural framework for quantum transport on complex networks. On regular structures, coin-walker entanglement has been widely used to characterize quantum transport and to support quantum algorithmic…

Quantum Physics · Physics 2026-05-04 Pravy Prerana , Sascha Wald

Quantum entanglement and its paradoxical properties hold the key to an information processing revolution. Much attention has focused recently on the challenging problem of characterizing entanglement. Entanglement for a two qubit system is…

Quantum Physics · Physics 2009-11-07 Vivien M Kendon , Kae Nemoto , William J Munro