Strongly Inhibited Transport of a Degenerate 1D Bose Gas in a Lattice

Abstract

We report the observation of strongly damped dipole oscillations of a quantum degenerate 1D atomic Bose gas in a combined harmonic and optical lattice potential. Damping is significant for very shallow axial lattices (0.25 photon recoil energies), and increases dramatically with increasing lattice depth, such that the gas becomes nearly immobile for times an order of magnitude longer than the single-particle tunneling time. Surprisingly, we see no broadening of the atomic quasimomentum distribution after damped motion. Recent theoretical work suggests that quantum fluctuations can strongly damp dipole oscillations of 1D atomic Bose gas, providing a possible explanation for our observations.PACS numbers: 03.75. Kk, 05.60.Gg, 73.43.Nq The ability of highly degenerate quantum systems to sustain dissipationless flow is one of the most striking manifestations of quantum mechanics. However, transport in such systems can be dramatically modified by the presence of a relatively weak, but rapidly spatially varying ("corrugated") potential along the transport axis. For example, the periodic potential of an optical lattice inhibits transport in a degenerate Fermi atomic gas [1, 2, 3], but not, in general, in a degenerate Bose gas (i.e., Bose-Einstein Condensate (BEC)) [4,5]. However, under certain conditions, highly dissipative transport in a BEC in an optical lattice [6,7,8] can arise from nonlinear dynamical instabilities [9,10,11]. In low dimensional systems, of which 1D atomic gases [12,13,14,15,16] and superconducting nanowires [17] are important experimentally realized examples, a corrugated potential can cause dramatic changes in ground state and transport properties.We study inhibited transport in a 1D Bose gas in the presence of an optical lattice along the 1D axis. In the absence of such a lattice, dipole oscillations are undamped [14], since it is a general result that the dipole mode of a harmonically confined gas is unaffected by 2-body interactions (generalized Kohn's theorem) [18]. This result does not strictly hold for a combined harmonic and periodic potential; nevertheless, undamped oscillations have been observed in 3D BECs for small amplitudes and weak interactions [5,19].In this Letter we report a study of strongly damped dipole oscillations of a 1D Bose gas in a combined harmonic and periodic potential, under conditions for which undamped motion has been observed previously for 3D BECs. This striking difference between 1D and 3D was recently reported, qualitatively, in Ref. [13]. Here we measure the damped motion as a function of axial lattice depth. Significant damping is induced by very shallow lattices, and in deeper lattices the motion is overdamped to the degree that the gas is nearly immobile for times an order of magnitude longer than the single-particle tunneling time. We emphasize, and discuss further below, that the inhibited transport is not due to Bloch oscillations [4,20], where transport is frustrated by Bragg reflection at the Brillouin zone (BZ) boundary, as has been seen in previou...

Quantum phase slips in one-dimensional superfluids in a periodic potential

“…While we have calculated the nucleation rate of quantum phase slips in order to characterize the superflow decay, it still remains ambiguous how the nucleation rate is related to the transport of 1D Bose gases in the presence of a trapping potential that has been studied in cold atom experiments [8][9][10][11]. Since the damping rate of the dipole oscillations has been often used to quantify the transport of trapped atomic gases, in our future work we will clarify direct connections of the nucleation rate with the damping rate.…”

“…Recently, superfluidity and superconductivity in one dimension (1D) have been experimentally studied in various systems, including superconducting nanowires [1][2][3][4][5], liquid helium in nanopores [6,7], and ultracold bosonic atoms in optical lattices [8][9][10][11]. A common property found in these different systems is that the transport in 1D is significantly suppressed compared to that in higher dimensions.…”

Self-trapping of Bose-Einstein condensates in optical lattices

“…In such a bosonic system, people have observed well-known and long predicted phenomena, such as Bloch oscillations [1] and the quantum phase transition between superfluid and Mottinsulator [2]. More importantly, there are new phenomena that have been either observed or predicted in this system, for example, nonlinear Landau-Zener tunneling between Bloch bands [3,4] and the strongly inhibited transport of one dimensional BEC in an optical lattice [5].…”

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“…varying laser intensities or magnetic fields. While first studies of dynamical properties of both bosonic and fermionic quantum gases [12][13][14] have already been performed, a remaining key challenge, however, has been the presence of additional potentials: These will lead to confining forces or, in the absence of interactions, to Bloch oscillations [15][16][17][18][19] that dominate transport.In this work, it was possible to study out-ofequilibrium dynamics and transport in a homogeneous Hubbard model by allowing an initially confined atomic cloud with variable interactions to expand freely within a arXiv:1005.3545v2 [cond-mat.quant-gas] …”