Measurement-based measure of the size of macroscopic quantum superpositions

Jan Ivar Korsbakken, K. Birgitta Whaley, Jonathan Dubois, and J. Ignacio Cirac
Phys. Rev. A 75, 042106 – Published 13 April 2007

Abstract

Recent experiments claiming the formation of quantum superposition states in near-macroscopic systems raise the question of how the sizes of general quantum superposition states in an interacting system are to be quantified. We propose here a measure of size for such superposition states that is based on what measurements can be performed to probe and distinguish the different branches of the state. The measure allows the comparison of the effective size for superposition states in very different physical systems. It can be applied to a very general class of superposition states and reproduces known results for near-ideal cases. Comparison with a prior measure based on analysis of coherence between branches indicates that significantly smaller effective superposition sizes result from our measurement-based measure. Application to a system of interacting bosons in a double-well trapping potential shows that the effective superposition size is strongly dependent on the relative magnitude of the barrier height and interparticle interaction.

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  • Received 7 November 2006

DOI:https://doi.org/10.1103/PhysRevA.75.042106

©2007 American Physical Society

Authors & Affiliations

Jan Ivar Korsbakken

  • Berkeley Center for Quantum Information and Computation, Department of Chemistry and Department of Physics, University of California, Berkeley, California 94720, USA

K. Birgitta Whaley and Jonathan Dubois

  • Berkeley Center for Quantum Information and Computation, Department of Chemistry, University of California, Berkeley, California 94720, USA

J. Ignacio Cirac

  • Max Planck Institut für Quantenoptik, Hans-Kopfermann Strasse 1, D-85748 Garching, Germany

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Issue

Vol. 75, Iss. 4 — April 2007

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