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Title

Quantum limits to center-of-mass measurements

Author(s)

Vaughan, Timothy;  Drummond, P. D.;  Leuchs, Gerd

Abstract

We discuss the issue of measuring the mean position (center of mass) of a group of bosonic or fermionic quantum particles, including particle number fluctuations. We introduce a standard quantum limit for these measurements at ultralow temperatures, and discuss this limit in the context of both photons and ultracold atoms. In the case of non-interacting harmonically trapped fermions, we present evidence that the Pauli exclusion principle has a strongly beneficial effect, giving rise to a 1 N scaling in the position standard deviation-as opposed to a 1 N scaling for bosons. The difference between the actual mean-position fluctuation and this limit is evidence for quantum wave-packet spreading in the center of mass. This macroscopic quantum effect cannot be readily observed for noninteracting particles, due to classical pulse broadening. For this reason, we also study the evolution of photonic and matter-wave solitons, where classical dispersion is suppressed. In the photonic case, we show that the intrinsic quantum diffusion of the mean position can contribute significantly to uncertainties in soliton pulse arrival times. We also discuss ways in which the relatively long lifetimes of attractive bosons in matter-wave solitons may be used to demonstrate quantum interference between massive objects composed of thousands of particles.

Publication type

Journal article

Source

Physical Review A, Vol. 75, no. 3 (2007), article no. 033617

Publication year

2007

FOR Code(s)

0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics;  0204 Condensed Matter Physics;  0205 Optical Physics

Keyword(s)

Atom lasers;  Boson systems;  Electron traps;  Fermion systems;  Fluctuations;  Harmonic analysis;  Light measurement;  Matter waves;  Particle number fluctuations;  Quantum interference phenomena;  Quantum optics;  Quantum particles;  Quantum theory;  Solitons;  Thermal effects;  Ultra low temperatures

Publisher

American Physical Society

ISSN

1050-2947

Publisher URL

http://dx.doi.org/10.1103/PhysRevA.75.033617

Copyright

Copyright © 2007 The American Physical Society. Published version of this paper reproduced here in accordance with the copyright policy of the publisher.

Full text

Peer reviewed