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Every measurement that can be implemented by local quantum operations and classical communication (LOCC) using an infinite number of rounds is the limit of a sequence of measurements each of which requires only a finite number of rounds.…

Quantum Physics · Physics 2014-10-14 Scott M. Cohen

Naive attempts to put together relativity and quantum measurements lead to signaling between space-like separated regions. In QFT, these are known as impossible measurements. We show that the same problem arises in non-relativistic quantum…

Quantum Physics · Physics 2024-02-28 Nicolas Gisin , Flavio Del Santo

We investigate universal features of measurement-and-feedback control of quantum chaotic dynamics by examining the quantum Arnold cat map, a paradigmatic model of quantum chaos. Inspired by probabilistic control of classical chaos, our…

Quantum Physics · Physics 2026-02-26 Andrew A. Allocca , Devesh K. Verma , Sriram Ganeshan , Justin H. Wilson

The idea that events obey a definite causal order is deeply rooted in our understanding of the world and at the basis of the very notion of time. But where does causal order come from, and is it a necessary property of nature? We address…

Quantum Physics · Physics 2013-02-15 Ognyan Oreshkov , Fabio Costa , Caslav Brukner

Nonlocality and its connections to entanglement are fundamental features of quantum mechanics that have found numerous applications in quantum information science. A set of correlations is said to be nonlocal if it cannot be reproduced by…

Quantum Physics · Physics 2023-11-30 Khashayar Barooti , Alexandru Gheorghiu , Grzegorz Głuch , Marc-Olivier Renou

In decentralized stochastic control (or stochastic team theory) and game theory, if there is a pre-defined order in a system in which agents act, the system is called \textit{sequential}, otherwise it is non-sequential. Much of the…

Optimization and Control · Mathematics 2025-08-05 Omar Mrani-Zentar , Ryan Simpson , Serdar Yüksel

Feedback-based control is the de-facto standard when it comes to controlling classical stochastic systems and processes. However, standard feedback-based control methods are challenged by quantum systems due to measurement induced…

Quantum Physics · Physics 2024-05-14 Kai Meinerz , Simon Trebst , Mark Rudner , Evert van Nieuwenburg

The coherent superposition of position states in a quantum walk (QW) can be precisely engineered towards the desired distributions to meet the need of quantum information applications. The coherent distribution can make full use of quantum…

The study of causal relations has recently been applied to the quantum realm, leading to the discovery that not all physical processes have a definite causal structure. While indefinite causal processes have previously been experimentally…

If two identical copies of a completely depolarizing channel are put into a superposition of their possible causal orders, they can transmit non-zero classical information. Here, we study how well we can transmit classical information with…

Quantum Physics · Physics 2021-06-23 Sk Sazim , Michal Sedlak , Kratveer Singh , Arun Kumar Pati

Indefinite causal order is a key feature involved in the study of quantum higher order transformations. Recently, intense research has been focused on possible advantages related to the lack of definite causal order of quantum processes.…

Quantum Physics · Physics 2023-06-12 Matheus Capela , Harshit Verma , Fabio Costa , Lucas Chibebe Céleri

Quantum theory is consistent with a computational model permitting black-box operations to be applied in an indefinite causal order, going beyond the standard circuit model of computation. The quantum switch -- the simplest such example --…

Bargmann invariants, multivariate traces of states, completely characterize any unitary-invariant property of a set of states. Unitary invariants enable the description of quantum resources such as basis-independent coherence and…

Quantum Physics · Physics 2025-08-05 Pedro C. Azado , Rafael Wagner , Rui S. Barbosa , Ernesto F. Galvão

In general relativity, `causal structure' refers to the partial order on space-time points (or regions) that encodes time-like relationships. Recently, quantum information and quantum foundations saw the emergence of a `causality…

Quantum Physics · Physics 2017-08-16 Aleks Kissinger , Matty Hoban , Bob Coecke

Quantum state verification provides an efficient approach to characterize the reliability of quantum devices for generating certain target states. The figure of merit of a specific strategy is the estimated infidelity $\epsilon$ of the…

The existence of incompatible measurements is often believed to be a feature of quantum theory which signals its inconsistency with any classical worldview. To prove the failure of classicality in the sense of Kochen-Specker…

Quantum Physics · Physics 2024-04-05 John H. Selby , David Schmid , Elie Wolfe , Ana Belén Sainz , Ravi Kunjwal , Robert W. Spekkens

Quantum incompatibility, referred as the phenomenon that some quantum measurements cannot be performed simultaneously, is necessary for various quantum information processing tasks, such as nonlocality and steering. When these applications…

Quantum Physics · Physics 2024-11-19 Xiaolin Zhang , Rui Qu , Zehong Chang , Yunlong Wang , Zhenyu Guo , Min An , Hong Gao , Fuli Li , Pei Zhang

We show that in principle, $N$-partite unitary transformations can be perfectly discriminated under local measurement and classical communication (LOCC) despite of their nonlocal properties. Based on this result, some related topics,…

Quantum Physics · Physics 2009-11-13 Xiangfa Zhou , Yongsheng Zhang , Guangcan Guo

Requiring that the causal structure between different parties is well-defined imposes constraints on the correlations they can establish, which define so-called causal correlations. Some of these are known to have a "dynamical" causal order…

Quantum Physics · Physics 2025-11-13 Raphaël Mothe , Alastair A. Abbott , Cyril Branciard

We present a categorical construction for modelling causal structures within a general class of process theories that include the theory of classical probabilistic processes as well as quantum theory. Unlike prior constructions within…

Quantum Physics · Physics 2023-06-22 Aleks Kissinger , Sander Uijlen