Multimode analysis of non-classical correlations in double-well Bose-Einstein condensates

Ferris, Andrew J. and Davis, Matthew J. (2010) Multimode analysis of non-classical correlations in double-well Bose-Einstein condensates. New Journal of Physics, 12 055024-1-055024-15. doi:10.1088/1367-2630/12/5/055024

Author Ferris, Andrew J.
Davis, Matthew J.
Title Multimode analysis of non-classical correlations in double-well Bose-Einstein condensates
Journal name New Journal of Physics   Check publisher's open access policy
ISSN 1367-2630
Publication date 2010-05-28
Sub-type Article (original research)
DOI 10.1088/1367-2630/12/5/055024
Open Access Status DOI
Volume 12
Start page 055024-1
End page 055024-15
Total pages 15
Place of publication Bristol, United Kingdom
Publisher Institute of Physics Publishing
Collection year 2011
Language eng
Subject 02 Physical Sciences
Formatted abstract
The observation of non-classical correlations arising in two weakly coupled Bose–Einstein condensates was recently reported by Estève et al (2008 Nature 455 1216). In order to observe relative number fluctuations between the two condensates below the standard quantum limit, they utilized the process of 'adiabatic passage' to drive the system out of thermal equilibrium. They found that this reduced the relative number fluctuations below that expected in thermal equilibrium at the minimum experimentally realizable temperature. We present a theoretical analysis that takes into account the spatial degrees of freedom of the system, allowing us to calculate the expected correlations at finite temperature in the system, and to verify the hypothesis of reduced number fluctuations via adiabatic passage by comparing the dynamics to the idealized model.

General Scientific Summary

Introduction and background:

Ultracold gases are examples of isolated quantum many-body systems, particularly useful for studying the dynamics of such systems. A recent experiment by Estève et al (2008 Nature 455 1216) demonstrated a non-classical correlation, called number squeezing, between two 'wells' of atoms. However, great care was required to achieve the low level of thermal uctuations required to observe this effect. In particular, they used a technique of 'effective cooling' to take the system out of thermal equilibrium, reducing the level of fluctuations between the wells at the cost of increasing the fluctuations within each well.

Main results:
Using both analytic and numeric approaches, we find that the technique of effective cooling works by the mechanism conjectured by Estève et al. In particular, the quantity of fluctuations present in each 'spatial mode' remains constant over the timescale of the experiment. By clever manipulation of the potential, and therefore the structure and energy of each spatial mode, one can achieve reduced fluctuations in the modes of interest—which in this case describe the population imbalance between the wells.

Wider implications:
In all but certain special cases, we expect classical and quantum systems to eventually equilibrate to a standard thermal distribution. What is remarkable is that we have found an example of a closed, three-dimensional, interacting quantum system that does not seem to approach thermal equilibrium, at least over the timescales investigated. Further, this behaviour can be understood with simple analytic arguments and is the basis of a useful experimental technique to reduce the effects of thermal fluctuations.
© IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Keyword Quantum gases
Liquids and solids
Atomic and molecular physics
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Mathematics and Physics
Official 2011 Collection
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Citation counts: TR Web of Science Citation Count  Cited 5 times in Thomson Reuters Web of Science Article | Citations
Scopus Citation Count Cited 3 times in Scopus Article | Citations
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Created: Sun, 27 Jun 2010, 00:03:29 EST