Connecting Berezinskii-Kosterlitz-Thouless and BEC Phase Transitions by Tuning Interactions in a Trapped Gas

Fletcher, R.; Robert-De-Saint-Vincent, Martin; Man, Jay; Navon, Nir; Smith, Robert P.; Viebahn, Konrad; Hadzibabic, Zoran

doi:10.1103/physrevlett.114.255302

Cited by 66 publications

(55 citation statements)

References 49 publications

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“…Experiments on 2D bosonic systems, such as a liquid helium film [16], and trapped Bose gases [17][18][19][20][21] have shown indications of the BKT transition. Furthermore, a trapped 2D system can form a BEC due to the modified density of states [22,23] and leads to an interesting interplay of the two phase transitions [24].…”

Section: Introductionmentioning

confidence: 99%

Superfluidity and relaxation dynamics of a laser-stirred two-dimensional Bose gas

et al. 2017

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We investigate the superfluid behavior of a two-dimensional (2D) Bose gas of 87 Rb atoms using classical field dynamics. In the experiment by R. Desbuquois et al., Nat. Phys. 8, 645 (2012), a 2D quasicondensate in a trap is stirred by a blue-detuned laser beam along a circular path around the trap center. Here, we study this experiment from a theoretical perspective. The heating induced by stirring increases rapidly above a velocity vc, which we define as the critical velocity. We identify the superfluid, the crossover, and the thermal regime by a finite, a sharply decreasing, and a vanishing critical velocity, respectively. We demonstrate that the onset of heating occurs due to the creation of vortex-antivortex pairs. A direct comparison of our numerical results to the experimental ones shows good agreement, if a systematic shift of the critical phase-space density is included. We relate this shift to the absence of thermal equilibrium between the condensate and the thermal wings, which were used in the experiment to extract the temperature. We expand on this observation by studying the full relaxation dynamics between the condensate and the thermal cloud.

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Section: Introductionmentioning

confidence: 99%

Superfluidity and relaxation dynamics of a laser-stirred two-dimensional Bose gas

et al. 2017

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“…Challenging open questions include (i) thermoelectric effects occurring through quantum evaporation, (ii) conductance quantization in 2D bosonic systems, where the quasicondensate enhances the role of interactions [35][36][37], and (iii) its impact in the presence of a superfluid, whose investigation has been initiated by recent experiments with strongly-interacting Fermi gases [9,38,39].…”

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confidence: 99%

Quantized conductance through the quantum evaporation of bosonic atoms

2016

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We analyze theoretically the quantization of conductance occurring with cold bosonic atoms trapped in two reservoirs connected by a constriction with an attractive gate potential. We focus on temperatures slightly above the condensation threshold in the reservoirs. We show that a conductance step occurs, coinciding with the appearance of a condensate in the constriction. Conductance relies on a collective process involving the quantum condensation of an atom into an elementary excitation and the subsequent quantum evaporation of an atom, in contrast with ballistic fermion transport. The value of the bosonic conductance plateau is strongly enhanced compared to fermions and explicitly depends on temperature. We highlight the role of the repulsive interactions between the bosons in preventing them from collapsing into the constriction.PACS numbers: 05.60. Gg,05.30.Jp, In mesoscopic systems, where the motion of quantum particles occurs over distances of the order of their coherence length, transport phenomena exhibit quantum signatures [1]. The quantization of conductance [2] is a hallmark among these effects. It reflects the discrete nature of the transport channels inside a strongly constricted geometry, and it occurs if the spread in energies of the incident particle distribution is smaller than the energy separation of these channels. It was first observed in electronic transport through a quantum point contact [3] as a series of plateaux in the conductance when the distance between the gate electrodes was increased. In this fermionic case, the conductance quantum G K = e 2 /h involves fundamental constants only, which makes it relevant for metrology [4, chap. 7]. Unlike the quantum Hall effect [5], it occurs in the absence of a magnetic field and has been predicted to affect neutral Helium atoms [6].Conductance quantization has recently been observed in ultracold fermionic gases [7]. Atomic gases allow for a clean observation in a simple setup involving two reservoirs connected by a constriction within which an attractive gate potential E G < 0 is varied (see Fig. 1). Experiments on ultracold fermions aim at simulating electronic systems using neutral particles [7][8][9][10]. In the fermionic experiment of Ref. [7], conductance quantization has been observed at temperatures much lower than both the Fermi temperature T F and the confinement energy of the constriction, in analogy with the original results on electronic transport [3] where only particles near the Fermi surface take part in transport phenomena. This raises the question of whether conductance quantization also affects bosons. Previous observations in an optical setup [11,12] and predictions with cold matter waves [13] have focused on systems where all particles have the same incident energy, mimicking fermionic transport at the Fermi energy. To our knowledge, the specific role of bosonic statistics in quantized conductance situations has not yet been investigated. Cold atom setups allow for theTwo reservoirs (L, R) can exchange particles through a s...

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“…Examples apart from 2D ultracold quantum gases [8][9][10][11][12] are given by thin Helium films [13], layered magnets [14,15], and 2D excitonpolariton condensates [16]. To quantify correlations in these systems we introduce the one-body density matrix ρ(r, r ) = Φ † (r)Φ(r ) , whereΦ † (r) is the creation operator for a particle at point r. For the spatially homogeneous case we then have ρ hom (r, r ) = f (|r − r |) with some function f (r) due to translation and rotation invariance.…”

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Quasi-long-range order in trapped two-dimensional Bose gases

Boettcher

Holzmann

2016

Phys. Rev. A

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We study the fate of algebraic decay of correlations in a harmonically trapped two-dimensional degenerate Bose gas. The analysis is inspired by recent experiments on ultracold atoms where power-law correlations have been observed despite the presence of the external potential. We generalize the spin wave description of phase fluctuations to the trapped case and obtain an analytical expression for the one-body density matrix within this approximation. We show that algebraic decay of the central correlation function persists to lengths of about 20% of the Thomas-Fermi radius. We establish that the trap-averaged correlation function decays algebraically with a strictly larger exponent weakly changing with trap size and find indications that the recently observed enhanced scaling exponents receive significant contributions from the normal component of the gas. We discuss radial and angular correlations and propose a local correlation approximation which captures the correlations very well. Our analysis goes beyond the usual local density approximation and the developed summation techniques constitute a powerful tool to investigate correlations in inhomogeneous systems.PACS numbers: 05.70. Jk, 64.60.an, With the achievement of quantum degeneracy in ultracold atom gases a new experimental platform for studying fundamental questions related to phase transitions and critical phenomena has appeared. In particular, correlation functions can be measured through interference and time-of-flight techniques [1][2][3][4][5][6][7]. A crucial aspect of the experiments, however, consists in the absence of translation invariance due to the presence of the external trapping potential. Consequently, correlations between points r and r are not uniquely determined by the value of r − r . This effect should be unimportant for short-range correlations, and, in fact, thermodynamic properties of ultracold gases are often very well-captured by a local density approximation. The situation changes drastically for a system at a critical point, where the correlation length diverges and thus competes with the inhomogeneity of the trapping potential.Whereas the experimental preparation of critical systems typically requires a highly fine-tuned setup, they are rather effortlessly realized in two-dimensional (2D) systems whose low-energy excitations can be mapped onto an XY model. Examples apart from 2D ultracold quantum gases [8][9][10][11][12] are given by thin Helium films [13], layered magnets [14,15], and 2D excitonpolariton condensates [16]. To quantify correlations in these systems we introduce the one-body density matrix ρ(r, r ) = Φ † (r)Φ(r ) , whereΦ † (r) is the creation operator for a particle at point r. For the spatially homogeneous case we then have ρ hom (r, r ) = f (|r − r |) with some function f (r) due to translation and rotation invariance. The Mermin-Wagner-Hohenberg theorem [17,18] forbids long-range order at any finite temperature such that lim r→∞ f (r) = 0. However, in the XY model an ordered low-temperature phase with inf...

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Connecting Berezinskii-Kosterlitz-Thouless and BEC Phase Transitions by Tuning Interactions in a Trapped Gas

Cited by 66 publications

References 49 publications

Superfluidity and relaxation dynamics of a laser-stirred two-dimensional Bose gas

Superfluidity and relaxation dynamics of a laser-stirred two-dimensional Bose gas

Quantized conductance through the quantum evaporation of bosonic atoms

Quasi-long-range order in trapped two-dimensional Bose gases

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