Two-dimensional supersolidity in a dipolar quantum gas

Abstract

Supersolidity -a quantum-mechanical phenomenon characterized by the presence of both superfluidity and crystalline order -was initially envisioned in the context of bulk solid helium, as a possible answer to the question of whether a solid could have superfluid properties [1][2][3][4][5]. While supersolidity has not been observed in solid helium (despite much effort)[6], ultracold atomic gases have provided a fundamentally new approach, recently enabling the observation and study of supersolids with dipolar atoms [7][8][9][10][11][12][13][14][15][16]. However, unlike the proposed phenomena in helium, these gaseous systems have so far only shown supersolidity along a single direction. By crossing a structural phase transition similar to those occurring in ionic chains [17][18][19][20], quantum wires [21,22], and theoretically in chains of individual dipolar particles [23,24], we demonstrate the extension of supersolid properties into two dimensions, providing an important step closer to the bulk situation envisioned in helium. This opens the possibility of studying rich excitation properties [25-28], including vortex formation [29][30][31], as well as ground-state phases with varied geometrical structure [7,32] in a highly flexible and controllable system.

Two-Dimensional Supersolid Formation in Dipolar Condensates

“…In the first dipolar supersolid experiments translational symmetry was broken only along one axis, giving rise to a one-dimensional (1D) density wave, commonly referred to as 1D droplet arrays [10][11][12]. A more recent experiment has created the first states with two-dimensional (2D) supersolidity in anisotropic traps of variable aspect ratio [16]. This opens the door to study vortices and persistent currents [17][18][19][20], as well as exotic ground state phases predicted for large atom numbers [21][22][23][24].…”

New opportunites for interactions and control with ultracold lanthanides

“…Following the demonstration of 1D supersolidity in dipolar gases, its two dimensional (2D) counterpart is currently attracting substantial renewed interest. Theoretically, recent studies have focused on the phase diagram and excitation spectra of 2D supersolid in isotropic and anisotropic traps [133][134][135], the possibility of such supersolids hosting vortices in the low-density regions [136][137][138], and on the formation of novel type of ground-states with exotic spatial patterns [133,139]. Very recently, supersolidity along two dimensions has been demonstrated in a trap of variable anisotropy [135].…”

“…Theoretically, recent studies have focused on the phase diagram and excitation spectra of 2D supersolid in isotropic and anisotropic traps [133][134][135], the possibility of such supersolids hosting vortices in the low-density regions [136][137][138], and on the formation of novel type of ground-states with exotic spatial patterns [133,139]. Very recently, supersolidity along two dimensions has been demonstrated in a trap of variable anisotropy [135]. In a related effort, an angular roton mode, analogous to the linear roton mode present in elongated traps, has been observed in a skittle shaped trap [98].…”

Maintaining supersolidity in one and two dimensions

“…While almost all dipolar supersolids have been experimentally realized as one-dimensional (1D) droplet arrays-see, for example, Refs. [10][11][12][13][14][15]-two recent experiments have for the first time created two-dimensional (2D) supersolids [29,30], thus opening an exciting frontier. An early theoretical study in 2D predicted a rich phase diagram determined by competing metastable crystal configurations [31].…”