Time and Spacetime: the Crystallizing Block Universe
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Elementary Explanation of the Inexistence of Decoherence at Zero
Elementary explanation of the inexistence of decoherence at zero temperature for systems with purely elastic scattering Yoseph Imry Dept. of Condensed-Matter Physics, the Weizmann Institute of science, Rehovot 76100, Israel (Dated: October 31, 2018) This note has no new results and is therefore not intended to be submitted to a ”research” journal in the foreseeable future, but to be available to the numerous individuals who are interested in this issue. Several of those have approached the author for his opinion, which is summarized here in a hopefully pedagogical manner, for convenience. It is demonstrated, using essentially only energy conservation and elementary quantum mechanics, that true decoherence by a normal environment approaching the zero-temperature limit is impossible for a test particle which can not give or lose energy. Prime examples are: Bragg scattering, the M¨ossbauer effect and related phenomena at zero temperature, as well as quantum corrections for the transport of conduction electrons in solids. The last example is valid within the scattering formulation for the transport. Similar statements apply also to interference properties in equilibrium. PACS numbers: 73.23.Hk, 73.20.Dx ,72.15.Qm, 73.21.La I. INTRODUCTION cally in the case of the coupling of a conduction-electron in a solid to lattice vibrations (phonons) 14 years ago [5] and immediately refuted vigorously [6]. Interest in this What diminishes the interference of, say, two waves problem has resurfaced due to experiments by Mohanty (see Eq. 1 below) is an interesting fundamental ques- et al [7] which determine the dephasing rate of conduc- tion, some aspects of which are, surprisingly, still being tion electrons by weak-localization magnetoconductance debated. -
Accommodating Retrocausality with Free Will Yakir Aharonov Chapman University, [email protected]
Chapman University Chapman University Digital Commons Mathematics, Physics, and Computer Science Science and Technology Faculty Articles and Faculty Articles and Research Research 2016 Accommodating Retrocausality with Free Will Yakir Aharonov Chapman University, [email protected] Eliahu Cohen Tel Aviv University Tomer Shushi University of Haifa Follow this and additional works at: http://digitalcommons.chapman.edu/scs_articles Part of the Quantum Physics Commons Recommended Citation Aharonov, Y., Cohen, E., & Shushi, T. (2016). Accommodating Retrocausality with Free Will. Quanta, 5(1), 53-60. doi:http://dx.doi.org/10.12743/quanta.v5i1.44 This Article is brought to you for free and open access by the Science and Technology Faculty Articles and Research at Chapman University Digital Commons. It has been accepted for inclusion in Mathematics, Physics, and Computer Science Faculty Articles and Research by an authorized administrator of Chapman University Digital Commons. For more information, please contact [email protected]. Accommodating Retrocausality with Free Will Comments This article was originally published in Quanta, volume 5, issue 1, in 2016. DOI: 10.12743/quanta.v5i1.44 Creative Commons License This work is licensed under a Creative Commons Attribution 3.0 License. This article is available at Chapman University Digital Commons: http://digitalcommons.chapman.edu/scs_articles/334 Accommodating Retrocausality with Free Will Yakir Aharonov 1;2, Eliahu Cohen 1;3 & Tomer Shushi 4 1 School of Physics and Astronomy, Tel Aviv University, Tel Aviv, Israel. E-mail: [email protected] 2 Schmid College of Science, Chapman University, Orange, California, USA. E-mail: [email protected] 3 H. H. Wills Physics Laboratory, University of Bristol, Bristol, UK. -
Quantum Theory Cannot Consistently Describe the Use of Itself
ARTICLE DOI: 10.1038/s41467-018-05739-8 OPEN Quantum theory cannot consistently describe the use of itself Daniela Frauchiger1 & Renato Renner1 Quantum theory provides an extremely accurate description of fundamental processes in physics. It thus seems likely that the theory is applicable beyond the, mostly microscopic, domain in which it has been tested experimentally. Here, we propose a Gedankenexperiment 1234567890():,; to investigate the question whether quantum theory can, in principle, have universal validity. The idea is that, if the answer was yes, it must be possible to employ quantum theory to model complex systems that include agents who are themselves using quantum theory. Analysing the experiment under this presumption, we find that one agent, upon observing a particular measurement outcome, must conclude that another agent has predicted the opposite outcome with certainty. The agents’ conclusions, although all derived within quantum theory, are thus inconsistent. This indicates that quantum theory cannot be extrapolated to complex systems, at least not in a straightforward manner. 1 Institute for Theoretical Physics, ETH Zurich, 8093 Zurich, Switzerland. Correspondence and requests for materials should be addressed to R.R. (email: [email protected]) NATURE COMMUNICATIONS | (2018) 9:3711 | DOI: 10.1038/s41467-018-05739-8 | www.nature.com/naturecommunications 1 ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/s41467-018-05739-8 “ 1”〉 “ 1”〉 irect experimental tests of quantum theory are mostly Here, | z ¼À2 D and | z ¼þ2 D denote states of D depending restricted to microscopic domains. Nevertheless, quantum on the measurement outcome z shown by the devices within the D “ψ ”〉 “ψ ”〉 theory is commonly regarded as being (almost) uni- lab. -
Geometric Phase from Aharonov-Bohm to Pancharatnam–Berry and Beyond
Geometric phase from Aharonov-Bohm to Pancharatnam–Berry and beyond Eliahu Cohen1,2,*, Hugo Larocque1, Frédéric Bouchard1, Farshad Nejadsattari1, Yuval Gefen3, Ebrahim Karimi1,* 1Department of Physics, University of Ottawa, Ottawa, Ontario, K1N 6N5, Canada 2Faculty of Engineering and the Institute of Nanotechnology and Advanced Materials, Bar Ilan University, Ramat Gan 5290002, Israel 3Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot 76100, Israel *Corresponding authors: [email protected], [email protected] Abstract: Whenever a quantum system undergoes a cycle governed by a slow change of parameters, it acquires a phase factor: the geometric phase. Its most common formulations are known as the Aharonov-Bohm, Pancharatnam and Berry phases, but both prior and later manifestations exist. Though traditionally attributed to the foundations of quantum mechanics, the geometric phase has been generalized and became increasingly influential in many areas from condensed-matter physics and optics to high energy and particle physics and from fluid mechanics to gravity and cosmology. Interestingly, the geometric phase also offers unique opportunities for quantum information and computation. In this Review we first introduce the Aharonov-Bohm effect as an important realization of the geometric phase. Then we discuss in detail the broader meaning, consequences and realizations of the geometric phase emphasizing the most important mathematical methods and experimental techniques used in the study of geometric phase, in particular those related to recent works in optics and condensed-matter physics. Published in Nature Reviews Physics 1, 437–449 (2019). DOI: 10.1038/s42254-019-0071-1 1. Introduction A charged quantum particle is moving through space. -
Annual Report to Industry Canada Covering The
Annual Report to Industry Canada Covering the Objectives, Activities and Finances for the period August 1, 2008 to July 31, 2009 and Statement of Objectives for Next Year and the Future Perimeter Institute for Theoretical Physics 31 Caroline Street North Waterloo, Ontario N2L 2Y5 Table of Contents Pages Period A. August 1, 2008 to July 31, 2009 Objectives, Activities and Finances 2-52 Statement of Objectives, Introduction Objectives 1-12 with Related Activities and Achievements Financial Statements, Expenditures, Criteria and Investment Strategy Period B. August 1, 2009 and Beyond Statement of Objectives for Next Year and Future 53-54 1 Statement of Objectives Introduction In 2008-9, the Institute achieved many important objectives of its mandate, which is to advance pure research in specific areas of theoretical physics, and to provide high quality outreach programs that educate and inspire the Canadian public, particularly young people, about the importance of basic research, discovery and innovation. Full details are provided in the body of the report below, but it is worth highlighting several major milestones. These include: In October 2008, Prof. Neil Turok officially became Director of Perimeter Institute. Dr. Turok brings outstanding credentials both as a scientist and as a visionary leader, with the ability and ambition to position PI among the best theoretical physics research institutes in the world. Throughout the last year, Perimeter Institute‘s growing reputation and targeted recruitment activities led to an increased number of scientific visitors, and rapid growth of its research community. Chart 1. Growth of PI scientific staff and associated researchers since inception, 2001-2009. -
Appendix: the Interaction Picture
Appendix: The Interaction Picture The technique of expressing operators and quantum states in the so-called interaction picture is of great importance in treating quantum-mechanical problems in a perturbative fashion. It plays an important role, for example, in the derivation of the Born–Markov master equation for decoherence detailed in Sect. 4.2.2. We shall review the basics of the interaction-picture approach in the following. We begin by considering a Hamiltonian of the form Hˆ = Hˆ0 + V.ˆ (A.1) Here Hˆ0 denotes the part of the Hamiltonian that describes the free (un- perturbed) evolution of a system S, whereas Vˆ is some added external per- turbation. In applications of the interaction-picture formalism, Vˆ is typically assumed to be weak in comparison with Hˆ0, and the idea is then to deter- mine the approximate dynamics of the system given this assumption. In the following, however, we shall proceed with exact calculations only and make no assumption about the relative strengths of the two components Hˆ0 and Vˆ . From standard quantum theory, we know that the expectation value of an operator observable Aˆ(t) is given by the trace rule [see (2.17)], & ' & ' ˆ ˆ Aˆ(t) =Tr Aˆ(t)ˆρ(t) =Tr Aˆ(t)e−iHtρˆ(0)eiHt . (A.2) For reasons that will immediately become obvious, let us rewrite this expres- sion as & ' ˆ ˆ ˆ ˆ ˆ ˆ Aˆ(t) =Tr eiH0tAˆ(t)e−iH0t eiH0te−iHtρˆ(0)eiHte−iH0t . (A.3) ˆ In inserting the time-evolution operators e±iH0t at the beginning and the end of the expression in square brackets, we have made use of the fact that the trace is cyclic under permutations of the arguments, i.e., that Tr AˆBˆCˆ ··· =Tr BˆCˆ ···Aˆ , etc. -
Quantum Violation of Classical Physics in Macroscopic Systems
Quantum VIOLATION OF CLASSICAL PHYSICS IN MACROSCOPIC SYSTEMS Lucas Clemente Ludwig Maximilian University OF Munich Max Planck INSTITUTE OF Quantum Optics Quantum VIOLATION OF CLASSICAL PHYSICS IN MACROSCOPIC SYSTEMS Lucas Clemente Dissertation AN DER Fakultät für Physik DER Ludwig-Maximilians-Universität München VORGELEGT VON Lucas Clemente AUS München München, IM NoVEMBER 2015 TAG DER mündlichen Prüfung: 26. Januar 2016 Erstgutachter: Prof. J. IGNACIO Cirac, PhD Zweitgutachter: Prof. Dr. Jan VON Delft WEITERE Prüfungskommissionsmitglieder: Prof. Dr. HarALD Weinfurter, Prof. Dr. Armin Scrinzi Reality is that which, when you stop believing in it, doesn’t go away. “ — Philip K. Dick How To Build A Universe That Doesn’t Fall Apart Two Days Later, a speech published in the collection I Hope I Shall Arrive Soon Contents Abstract xi Zusammenfassung xiii List of publications xv Acknowledgments xvii 0 Introduction 1 0.1 History and motivation . 3 0.2 Local realism and Bell’s theorem . 5 0.3 Contents of this thesis . 10 1 Conditions for macrorealism 11 1.1 Macroscopic realism . 13 1.2 Macrorealism per se following from strong non-invasive measurability 15 1.3 The Leggett-Garg inequality . 17 1.4 No-signaling in time . 19 1.5 Necessary and sufficient conditions for macrorealism . 21 1.6 No-signaling in time for quantum measurements . 25 1.6.1 Without time evolution . 26 1.6.2 With time evolution . 27 1.7 Conclusion and outlook . 28 Appendix 31 1.A Proof that NSIT0(1)2 is sufficient for NIC0(1)2 . 31 2 Macroscopic classical dynamics from microscopic quantum behavior 33 2.1 Quantifying violations of classicality . -
Particle Or Wave: There Is No Evidence of Single Photon Delayed Choice
Particle or wave: there is no evidence of single photon delayed choice. Michael Devereux* Los Alamos National Laboratory (Retired) Abstract Wheeler supposed that the way in which a single photon is measured in the present could determine how it had behaved in the past. He named such retrocausation delayed choice. Over the last forty years many experimentalists have claimed to have observed single-photon delayed choice. Recently, however, researchers have proven that the quantum wavefunction of a single photon assumes the identical mathematical form of the solution to Maxwell’s equations for that photon. This efficacious understanding allows for a trenchant analysis of delayed-choice experiments and denies their retrocausation conclusions. It is now usual for physicists to employ Bohr’s wave-particle complementarity theory to distinguish wave from particle aspects in delayed- choice observations. Nevertheless, single-photon, delayed-choice experiments, provide no evidence that the photon actually acts like a particle, or, instead, like a wave, as a function of a future measurement. And, a recent, careful, Stern-Gerlach analysis has shown that the supposition of concurrent wave and particle characteristics in the Bohm-DeBroglie theory is not tenable. PACS 03.65.Ta, 03.65.Ud 03.67.-a, 42.50.Ar, 42.50.Xa 1. Introduction. Almost forty years ago Wheeler suggested that there exists a type of retrocausation, which he called delayed choice, in certain physical phenomena [1]. Specifically, he said that the past behavior of some quantum systems could be determined by how they are observed in the present. “The past”, he wrote, “has no existence except as it is recorded in the present” [2]. -
David Bohn, Roger Penrose, and the Search for Non-Local Causality
David Bohm, Roger Penrose, and the Search for Non-local Causality Before they met, David Bohm and Roger Penrose each puzzled over the paradox of the arrow of time. After they met, the case for projective physical space became clearer. *** A machine makes pairs (I like to think of them as shoes); one of the pair goes into storage before anyone can look at it, and the other is sent down a long, long hallway. At the end of the hallway, a physicist examines the shoe.1 If the physicist finds a left hiking boot, he expects that a right hiking boot must have been placed in the storage bin previously, and upon later examination he finds that to be the case. So far, so good. The problem begins when it is discovered that the machine can make three types of shoes: hiking boots, tennis sneakers, and women’s pumps. Now the physicist at the end of the long hallway can randomly choose one of three templates, a metal sheet with a hole in it shaped like one of the three types of shoes. The physicist rolls dice to determine which of the templates to hold up; he rolls the dice after both shoes are out of the machine, one in storage and the other having started down the long hallway. Amazingly, two out of three times, the random choice is correct, and the shoe passes through the hole in the template. There can 1 This rendition of the Einstein-Podolsky-Rosen, 1935, delayed-choice thought experiment is paraphrased from Bernard d’Espagnat, 1981, with modifications via P. -
2. Superoscillations.Pdf
When the Whole Vibrates Faster than Any of its Parts Computational Superoscillation Theory Nicholas Wheeler December 2017 Introduction. The phenomenon/theory of “superoscillations”—brought to my attention by my friend Ahmed Sebbar1—originated in the time-symmetric formulation of quantum mechanics2 that gave rise to the theory of “weak measurements.” Recognition of the role that superoscillations play in that work was brought into explicit focus by Aharonov et al in 1990, and since that date the concept has found application to a remarkable variety of physical subject areas. Yakir Aharonov took his PhD in 1960 from the University of Bristol, where he worked with David Bohm.3 In 1992 a conference was convened at Bristol to celebrate Aharonov’s 60th birthday. It was on that occasion that the superoscillation phenomenon came first to the attention of Michael Berry (of the Bristol faculty), who in an essay “Faster than Fourier” contributed to the proceedings of that conference4 wrote that “He [Aharonov] told me that it is possible for functions to oscillate faster than any of their Fourier components. This seemed unbelievable, even paradoxical; I had heard nothing like it before. ” Berry was inspired to write a series of papers relating to the theory of superoscillation and its potential applications, as also by now have a great many other authors. 1 Private communication, 17 November 2017. 2 Y. Aharonov, P. G. Bergmann & J. L. Libowitz, “Time symmetry in the quantum meassurement process,” Phys. Rev. B 134, 1410–1416 (1964). 3 It was, I suspect, at the invitation of E. P Gross—who had collaborated with Bohm when both were at Princeton—that Aharonov spent 1960–1961 at Brandeis University, from which I had taken the first PhD and departed to Utrecht/CERN in February of 1960, so we never met. -
New Journal of Physics the Open–Access Journal for Physics
New Journal of Physics The open–access journal for physics The rise and fall of redundancy in decoherence and quantum Darwinism C Jess Riedel1,2,5, Wojciech H Zurek1,3 and Michael Zwolak1,4 1 Theoretical Division/CNLS, LANL, Los Alamos, NM 87545, USA 2 Department of Physics, University of California, Santa Barbara, CA 93106, USA 3 Santa Fe Institute, Santa Fe, NM 87501, USA 4 Department of Physics, Oregon State University, Corvallis, OR 97331, USA E-mail: [email protected] New Journal of Physics 14 (2012) 083010 (20pp) Received 9 March 2012 Published 10 August 2012 Online at http://www.njp.org/ doi:10.1088/1367-2630/14/8/083010 Abstract. A state selected at random from the Hilbert space of a many-body system is overwhelmingly likely to exhibit highly non-classical correlations. For these typical states, half of the environment must be measured by an observer to determine the state of a given subsystem. The objectivity of classical reality—the fact that multiple observers can agree on the state of a subsystem after measuring just a small fraction of its environment—implies that the correlations found in nature between macroscopic systems and their environments are exceptional. Building on previous studies of quantum Darwinism showing that highly redundant branching states are produced ubiquitously during pure decoherence, we examine the conditions needed for the creation of branching states and study their demise through many-body interactions. We show that even constrained dynamics can suppress redundancy to the values typical of random states on relaxation timescales, and prove that these results hold exactly in the thermodynamic limit. -
How the Many Worlds Interpretation Brings Common Sense to Paradoxical Quantum Experiments
How the Many Worlds Interpretation brings Common Sense to Paradoxical Quantum Experiments Kelvin J. McQueen and Lev Vaidman The many worlds interpretation of quantum mechanics (MWI) states that the world we live in is just one among many parallel worlds. It is widely believed that because of this commitment to parallel worlds, the MWI violates common sense. Some go so far as to reject the MWI on this basis. This is despite its myriad of advantages to physics (e.g. consistency with relativity theory, mathematical simplicity, realism, determinism, etc.). Here, we make the case that common sense in fact favors the MWI. We argue that causal explanations are commonsensical only when they are local causal explanations. We present several quantum mechanical experiments that seem to exhibit nonlocal “action at a distance”. Under the assumption that only one world exists, these experiments seem immune to local causal explanation. However, we show that the MWI, by taking all worlds together, can provide local causal explanations of the experiments. The MWI therefore restores common sense to physical explanation. 1. Introduction The purpose of explanation is to help us understand why things happen as they do. Typically, one explains an event by citing the causes of that event. For example, to explain why the window broke, one might cite the throwing of a stone. A particularly compelling and natural type of causal explanation is local causal explanation. In a local causal explanation there is spatiotemporal continuity between the cause and the explained effect. For example, the thrown stone explains the broken window in part because the stone traces out a continuous trajectory from the stone-thrower’s hand to the window.