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This is a book about operational probabilistic theories. The standard approach in such theories is from a time forward perspective. In this book we mostly take a time symmetric perspective. This presents a branding problem. Is this a niche…

Quantum Physics · Physics 2026-03-27 Lucien Hardy

There is a deep structural link between acausal spacetimes and quantum theory. As a consequence quantum theory may resolve some "paradoxes" of time travel. Conversely, non-time-orientable spacetimes naturally give rise to electric charges…

General Relativity and Quantum Cosmology · Physics 2007-05-23 Mark J Hadley

We characterize the conditions under which a multi-time quantum process with a finite temporal resolution can be approximately described by an equilibrium one. By providing a generalization of the notion of equilibration on average, where a…

Quantum Physics · Physics 2020-10-02 Pedro Figueroa-Romero , Kavan Modi , Felix A. Pollock

Quantum causality extends the conventional notion of fixed causal structure by allowing channels and operations to act in an indefinite causal order. The importance of such an indefinite causal order ranges from the foundational---e.g.…

Quantum Physics · Physics 2020-09-29 K. Goswami , J. Romero

Because of the non-locality of quantum entanglement, realist approaches to completing quantum mechanics have implications for our conception of space. Quantum gravity also is expected to predict phenomena in which the locality of classical…

History and Philosophy of Physics · Physics 2018-06-01 Lee Smolin

Time reversal in a macroscopic system is contradicting daily experience. It is practically impossible to restore a shattered cup to its original state by just time reversing the microscopic dynamics that led to its breakage. Yet, with the…

I provide an alternative way of seeing quantum computation. First, I describe an idealized classical problem solving machine that, thanks to a many body interaction, reversibly and nondeterministically produces the solution of the problem…

Quantum Physics · Physics 2007-10-10 Giuseppe Castagnoli

Communication in a network generally takes place through a sequence of intermediate nodes connected by communication channels. In the standard theory of communication, it is assumed that the communication network is embedded in a classical…

This work investigates the quantum transport in a narrow constriction acted upon by a finite-range transversely polarized time-dependent electric field. A generalized scattering-matrix method is developed that has incorporated a…

Mesoscale and Nanoscale Physics · Physics 2009-11-11 C. S. Tang , C. S. Chu

We treat space and time as bona fide quantum degrees of freedom on an equal footing in Hilbert space. Motivated by considerations in quantum gravity, we focus on a paradigm dealing with linear, first-order Hamiltonian and momentum…

Quantum Physics · Physics 2022-01-19 Ashmeet Singh

Fundamental interactions are either fully or nearly symmetric under time reversal. But macroscopic phenomena have a definite arrow of time. Though there is no convergence on the origin of time's preferential direction, many researchers…

Fluid Dynamics · Physics 2019-11-25 Mahendra K. Verma

We propose a new point of view regarding the problem of time in quantum mechanics, based on the idea of replacing the usual time operator $\mathbf{T}$ with a suitable real-valued function $T$ on the space of physical states. The proper…

Recently, there has been substantial interest in studying the dynamics of quantum theory beyond that of states, in particular, the dynamics of channels, measurements, and higher-order transformations. Ref. [Phys. Rev. X 8(1), 011047 (2018)]…

Quantum Physics · Physics 2024-08-06 John H. Selby , Ana Belén Sainz , Paweł Horodecki

The quantum strategy (or quantum combs) framework is a useful tool for reasoning about interactions among entities that process and exchange quantum information over the course of multiple turns. We prove a time-reversal property for a…

Quantum Physics · Physics 2018-10-22 Yuan Su , John Watrous

We present a number of new physical systems that may be addressed using methods of time dependent transformation. A recap of results available for two-state systems is given, with particular emphasis on the AC stark effect. We give some…

Quantum Physics · Physics 2023-06-05 Peter Morrison

We introduce a protocol for a quantum switch in the gravitational field of a spherical mass and determine the time interval required for its realization in the gravity of Earth. One of the agents that perform operations with indefinite…

Quantum Physics · Physics 2021-10-19 Natália S. Móller , Bruna Sahdo , Nelson Yokomizo

The linear superposition principle in quantum mechanics is essential for several no-go theorems such as the no-cloning theorem, the no-deleting theorem and the no-superposing theorem. It remains an open problem of finding general forbidden…

Quantum Physics · Physics 2018-06-26 Ming-Xing Luo , Hui-Ran Li , Hong Lai , Xiaojun Wang

Quantum teleportation is a very helpful information-theoretic protocol that allows to transfer an unknown arbitrary quantum state from one location to another without having to transmit the quantum system through the intermediate region.…

Quantum Physics · Physics 2022-03-02 Marius Krumm , Philippe Allard Guérin , Thomas Zauner , Časlav Brukner

Usual quantum mechanics requires a fixed, background, spacetime geometry and its associated causal structure. A generalization of the usual theory may therefore be needed at the Planck scale for quantum theories of gravity in which…

General Relativity and Quantum Cosmology · Physics 2013-12-05 James B. Hartle

Parametric correlations of energy spectra of quantum chaotic systems are presented in the orthogonal-unitary and symplectic-unitary crossover region. The spectra are allowed to disperse as a function of two external perturbations: one of…

Condensed Matter · Physics 2009-10-22 N. Taniguchi , A. Hashimoto , B. D. Simons , B. L. Altshuler