Berezinskii–Kosterlitz–Thouless crossover in a trapped atomic gas

By Z. Hadzibabic, P. Krüger, M. Cheneau, B. Battelier, J. Dalibard. Nature, 2006

729 citations recorded by the source corpus.

Any state of matter is classified according to its order, and the type of order that a physical system can possess is profoundly affected by its dimensionality. Conventional long-range order, as in a ferromagnet or a crystal, is common in three-dimensional systems at low temperature. However, in two-dimensional systems with a continuous symmetry, true long-range order is destroyed by thermal fluctuations at any finite temperature. Consequently, for the case of identical bosons, a uniform two-dimensional fluid cannot undergo Bose–Einstein condensation, in contrast to the three-dimensional case. However, the two-dimensional system can form a ‘quasi-condensate’ and become superfluid below a finite critical temperature. The Berezinskii–Kosterlitz–Thouless (BKT) theory associates this phase transition with the emergence of a topological order, resulting from the pairing of vortices with opposite circulation. Above the critical temperature, proliferation of unbound vortices is expected. Here we report the observation of a BKT-type crossover in a trapped quantum degenerate gas of rubidium atoms. Using a matter wave heterodyning technique, we observe both the long-wavelength fluctuations of the quasi-condensate phase and the free vortices. At low temperatures, the gas is quasi-coherent on the length scale set by the system size. As the temperature is increased, the loss of long-range coherence coincides with the onset of proliferation of free vortices. Our results provide direct experimental evidence for the microscopic mechanism underlying the BKT theory, and raise new questions regarding coherence and superfluidity in mesoscopic systems.

Subfields: Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/637237ed9e79affffd356d557e58f1e98a2266e0

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Citations in the corpus

Less is Different: Emergence and Reduction Reconciled (2011, background): “Yeomans [81], p. 112; Cardy [18], pp. 61, 69–72; Chaikin and Lubensky [21], pp. 216, 270–273; Hadzibabic et al. [ 35 ] is a recent example of experiments).”
Probing quantum and thermal noise in an interacting many-body system (2007, methodology): “Interference experiments provide a different powerful tool which allowed, for example, the study of macroscopic phase coherence [14], critical fluctuations [15], thermal fluctuations in elongated condensates [16], and the Berezinskii-Kosterlitz-Thouless transition in a twodimensional quantum gas [17”
Obtaining the phase diagram and thermodynamic quantities of bulk systems from the densities of trapped gases (2008, background): “It is a quantity particularly important for 2D superfluid”
Bose–Einstein condensation of photons in an optical microcavity (2010, methodology): “ relevant [17]. This is supported by an experiment directing the condensate peak through a sheer interferometer, where we have not seen signatures of phase blurring expected for a KT phase transition [18]. To test for the predicted variation of the phase transition onset, following eq. 1, we have va”
Suppression of the critical temperature for superfluidity near the Mott transition (2009, positive): “Ultracold bosonic atoms in optical lattices have sparked investigations of strongly correlated many-body quantum phases with ultracold atoms [1, 2, 3] that are now at the forefront of current research [4, 5, 6, 7].”
Rotating trapped Bose-Einstein condensates (2008, background): “In a recent experiment at ENS (Paris), Hadzibabic et al. (2006) apply a standing-wave laser field perpendicular to the symmetry axis of a cigar-shaped condensate, splitting the atoms into two essentially independent thin pancake strips with lateral dimensions ≈ 120 µm×10 µm.”
New perspectives for Rashba spin-orbit coupling. (2015, methodology): “Examples of groundbreaking experiments in this respect are the exploration of the crossover between Bose-Einstein and Bardeen-Cooper-Schrieffer regimes of fermion pair condensations [145], the observation of vortex unbinding in two-dimensions [146], and the Mott insulator-to-superfluid quantum phase”
Theory of ultracold atomic Fermi gases (2007, methodology): “…al., 2004); the realization of low dimensional configurations, including the 1D TonksGirardeau gas (Kinoshita, Wenger and Weiss, 2004; Paredes et al., 2004) and the Berezinskii-Kosterlitz-Thouless phase transition in 2D configurations (Hadzibabic et al., 2006; Schweikhard, Tung and Cornell, 2007).”