Long-Lived and Transient Supersolid Behaviors in Dipolar Quantum Gases

Abstract

By combining theory and experiments, we demonstrate that dipolar quantum gases of both 166 Er and 164 Dy support a state with supersolid properties, where a spontaneous density modulation and a global phase coherence coexist. This paradoxical state occurs in a well defined parameter range, separating the phases of a regular Bose-Einstein condensate and of an insulating droplet array, and is rooted in the roton mode softening, on the one side, and in the stabilization driven by quantum fluctuations, on the other side. Here, we identify the parameter regime for each of the three phases. In the experiment, we rely on a detailed analysis of the interference patterns resulting from the free expansion of the gas, quantifying both its density modulation and its global phase coherence. Reaching the phases via a slow interaction tuning, starting from a stable condensate, we observe that 166 Er and 164 Dy exhibit a striking difference in the lifetime of the supersolid properties, due to the different atom loss rates in the two systems. Indeed, while in 166 Er the supersolid behavior only survives a few tens of milliseconds, we observe coherent density modulations for more than 150 ms in 164 Dy. Building on this long lifetime, we demonstrate an alternative path to reach the supersolid regime, relying solely on evaporative cooling starting from a thermal gas. arXiv:1903.04375v1 [cond-mat.quant-gas]

Berezinskii-Kosterlitz-Thouless transition in two-dimensional dipolar stripes

“…Still in the context of ultracold gases, dipolar systems have been postulated as good candidates to the supersolid state. In fact, supersolid signatures have been observed by several groups [5][6][7], following previous theoretical work [8]. Recently, the gapless Goldstone excitation has also been measured for the same system [9][10][11].…”

“…[ε0] ns/n(Tc) 0.01 0.0 1.316(6) 0.838(4) 25 0.0 1.282(8) 0.816(6) 0.01 0.2 1.317(3) 0.838(6) 25 0.2 1.292(5) 0.823(4) 0.01 0.4 1.29(11) 0.821(6) 25 0.4 1.322(1) 0.842(3) 0.01 0.6 1.263(13) 0.804(8) 25 0.6 1.347(3) 0.BKT critical temperatures (in dipolar units) for different values of the density nr 2 0 and tilting angle α, in both the gas and stripe phases. The superfluid fraction at the critical temperature is evaluated through Eq.…”

Excitation spectrum and supersolidity of a two-leg bosonic ring ladder

“…The concept of supersolidity was first introduced in the context of liquid Helium more than fifty years ago [1,2]. With ultracold atoms, supersolidity has been observed with Bose-Einstein condensates in a cavity [3][4][5][6] as well as in dipolar quantum gases [7][8][9][10]. Both experimental realizations of supersolidity are based on longrange interactions [11], a key ingredient first introduced by Gross [12].…”

Coherent spin mixing via spin-orbit coupling in Bose gases

“…Such spin-orbit coupled gases are characterized by parameterdependent nontrivial single-particle dispersion relations. In an interplay with the inter-atomic interactions, these yield a rich phase diagram, including a zero-momentum phase, a spin-polarized phase and a spatially modulated phase with supersolid-like properties [5][6][7][8] (for supersolid phases from magnetic interactions see [9][10][11]). Likewise, the presence of SOC notably affects the dynamics of the gas, with an excitation spectrum exhibiting peculiar features such as anisotropy, suppression of the sound velocity or the emergence of a roton minimum in the planewave phase [12][13][14][15].…”