Anisotropic Superfluid Behavior of a Dipolar Bose-Einstein Condensate

Abstract

We present transport measurements on a dipolar superfluid using a Bose-Einstein condensate of ^{162}Dy with strong magnetic dipole-dipole interactions. By moving an attractive laser beam through the condensate we observe an anisotropy in superfluid flow. This observation is compatible with an anisotropic critical velocity for the breakdown of dissipationless flow, which, in the spirit of the Landau criterion, can directly be connected to the anisotropy of the underlying dipolar excitation spectrum. In addition, the heating rate above this critical velocity reflects the same anisotropy. Our observations are in excellent agreement with simulations based on the Gross-Pitaevskii equation and highlight the effect of dipolar interactions on macroscopic transport properties, rendering dissipation anisotropic.

Long-Lived and Transient Supersolid Behaviors in Dipolar Quantum Gases

“…This is found to be an appropriate description from an analysis of the density profiles of Fig. 1(b-d); see also [46]. For two droplets at a distance d and of identical Gaus-sian widths, σ y , along the array direction, S is simply S = exp(−d 2 /4σ 2 y ).…”

“…Following the work of Ref. [46], we perform a first estimate of the tunneling coefficient by simply considering the single-particle part of the Hamiltonian and evaluate it between two neighboring droplets. We note that, in our particular setting where the density modulation is not externally imposed but arises from the mere interparticle interactions, the inter-droplet interaction may also play a crucial role.…”

“…Generalizing the description of Ref. [46] to neighboring droplets of different sizes and amplitudes, which are described by a three-dimensional wavefunction ψ i (r) approximated to a three-dimensional Gaussian of widths (σ i,x , σ i,y , σ i,z ) with σ i,y = σ i , our estimate writes:…”

Vortex lattice formation in dipolar Bose-Einstein condensates via rotation of the polarization

“…In particular, dipolar quantum gases such as dipolar Bose-Einstein condensates (BECs) and degenerate dipolar fermionic gases offer a unique route to novel many-body phenomena where the subtle interplay between long-and short-range interactions plays a significant role [1][2][3], and considerable progress has been made in the study of dipolar BECs in the last two decades. After the first dipolar BEC was produced using chromium in 2005 [4], the effects of the dipolar interaction on the stability and excitations of the condensate were of much interest, with particular focus on the anisotropy of the condensate's superfluidity [5][6][7] and the theoretical possibility of roton modes and supersolidity [8,9]. More recently the production of dysprosium and erbium BECs, which feature considerably stronger dipolar interactions than Cr BECs, has led to the discovery of an increasingly diverse range of exotic phenomena [10,11].…”

Self-Bound Doubly Dipolar Bose-Einstein Condensates

“…Although these studies have been mostly restricted to paramagnetic polar molecules [25][26][27][28], a recent proposal has discussed the feasibility of realizing an electric, in addition to the magnetic, dipole moment in Dy atoms [20]. The latter is particularly important step due to the experimental feasibilities in atom-based setups, and opens intriguing questions about the effect of doubly dipole-dipole interactions (DDDIs) in quantum gases.Due to its anisotropic and long-range nature, dipole-dipole interaction (DDI) results in novel phenomena in DBECs [7][8][9], including anisotropic superfluidity [29][30][31], roton-like excitations [32,33], quantum droplets [34-37] and transient supersolid states [38][39][40]. Quantum droplets have been the focus of large attention, since they result from the stabilization due to quantum fluctuations of an otherwise collapsing DBEC.In this letter, we discuss the novel physics of condensates of particles with both magnetic and electric dipole moments.…”