Evidence for an oscillating soliton/vortex ring by density engineering of a Bose–Einstein condensate

Abstract

When two Bose-Einstein condensates (BEC's) collide with high collisional energy, the celebrated matter wave interference pattern results. For lower collisional energies the repulsive interaction energy becomes significant, and the interference pattern evolves into an array of grey solitons. The lowest collisional energy, producing a single pair of solitons, has not been probed. We use density engineering on the healing length scale to produce such a pair of solitons. These solitons then evolve periodically between vortex rings and solitons, which we image in-situ on the healing length scale. The stable, periodic evolution is in sharp contrast to the behavior of previous experiments, in which the solitons decay irreversibly into vortex rings via the snake instability. The evolution can be understood in terms of conservation of mass and energy in a narrow condensate. The periodic oscillation between two qualitatively different forms seems to be a rare phenomenon in nature.

Spontaneous creation of Kibble–Zurek solitons in a Bose–Einstein condensate

“…More solitons are shown in the other panels, including cases where the solitonic planes are bent and/or collide as in f) and g). As opposed to artificially created solitons via phase imprinting techniques [27][28][29] or by exciting the superfluid with laser pulses or through collisions [30,31], our solitons spontaneously form when the BEC is created by crossing the transition temperature.The identification of these defects as dark/grey solitons is based on several arguments: they are simultaneously observed as lines from two orthogonal directions in the radial plane, demonstrating their planar structure, mostly perpendicular to the weak axis of confinement; sometimes they exhibit a bent shape as we expect for snake oscillations [32] of soliton planes; when two of these defects overlap, they appear as solitons in a collision [33], whose individual structure is preserved except in the crossing region. Finally their size after TOF is of the right order of magnitude.…”

Generic equilibration dynamics of planar defects in trapped atomic superfluids

“…In addition to suggesting directions for future experimental research, these studies yield further insight into related past experiments and simulations [1][2][3][4][5][6]. In the process we clarify the many different defect sequences which have been reported in the literature.…”

“…What we show here is that the decay of extended planar defects involves vortex rings. But these rings are not the endproduct of a process in which the plane disappears, nor are they in general associated with a "soliton-ring oscillation" process [1]. Rather there is a co-existence of phase wall with near-trap-edge vortex rings which repeatedly enter and exit the trap.…”

“…While these were designed to measure the speed of sound, these studies very early on elicited somewhat controversial [11] theoretical suggestions that dark solitons had been created in the process [3,[12][13][14][15]. Similar experiments have led to the observation of a variety of defects [1,[16][17][18], while other studies engineered localized excitations through phase imprinting [4][5][6][19][20][21]. The theory associated with these experiments has suggested that solitons, or vortices or vortex rings (in some combination or sequentially) are created in the process [4,[6][7][8][22][23][24][25].…”

“…These include the report of a so-called oscillating soliton-vortex ring [1] created with a density depletion, while in a more complicated system of two density defects, there are claims of structures that involved both solitons and vortex rings [17]. Both phase imprinting and density depletions have led to reports of multiple solitons that bent significantly and in some cases decayed to vortices [16,20].…”