Models of wave-function collapse, underlying theories, and experimental tests

Angelo Bassi, Kinjalk Lochan, Seema Satin, Tejinder P. Singh, and Hendrik Ulbricht
Rev. Mod. Phys. 85, 471 – Published 2 April 2013
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Abstract

Quantum mechanics is an extremely successful theory that agrees with every experimental test. However, the principle of linear superposition, a central tenet of the theory, apparently contradicts a commonplace observation: macroscopic objects are never found in a linear superposition of position states. Moreover, the theory does not explain why during a quantum measurement, deterministic evolution is replaced by probabilistic evolution, whose random outcomes obey the Born probability rule. In this article a review is given of an experimentally falsifiable phenomenological proposal, known as continuous spontaneous collapse: a stochastic nonlinear modification of the Schrödinger equation, which resolves these problems, while giving the same experimental results as quantum theory in the microscopic regime. Two underlying theories for this phenomenology are reviewed: trace dynamics and gravity-induced collapse. As the macroscopic scale is approached, predictions of this proposal begin to differ appreciably from those of quantum theory and are being confronted by ongoing laboratory experiments that include molecular interferometry and optomechanics. These experiments, which test the validity of linear superposition for large systems, are reviewed here, and their technical challenges, current results, and future prospects summarized. It is likely that over the next two decades or so, these experiments can verify or rule out the proposed stochastic modification of quantum theory.

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  • Received 21 June 2012

DOI:https://doi.org/10.1103/RevModPhys.85.471

© 2013 American Physical Society

Authors & Affiliations

Angelo Bassi*

  • Department of Physics, University of Trieste, Strada Costiera 11, 34151 Trieste, Italy and Istituto Nazionale di Fisica Nucleare, Trieste Section, Via Valerio 2, 34127 Trieste, Italy

Kinjalk Lochan

  • Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India

Seema Satin

  • Institute of Mathematical Sciences, IV Cross Road, CIT Campus, Taramani, Chennai 600 113, India

Tejinder P. Singh§

  • Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India

Hendrik Ulbricht

  • School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, United Kingdom

  • *bassi@ts.infn.it
  • kinjalk@tifr.res.in
  • satin@imsc.res.in
  • §tpsingh@tifr.res.in
  • h.ulbricht@soton.ac.uk

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Issue

Vol. 85, Iss. 2 — April - June 2013

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