Pinning of hidden vortices in Bose-Einstein condensates

Abstract

We study the vortex dynamics and vortex pinning effect in Bose-Einstein condensate in a rotating double-well trap potential and co-rotating optical lattice. We show that, in agreement with the experiment, the vortex number do not diverge when the rotational frequency Ω → 1 if the trap potential is of anisotropic double-well type. The critical rotational frequency as obtained from numerical simulations agrees very well with the value √ l/l for l = 4 which supports the conjecture that surface modes with angular momentum l = 4 are excited when the rotating condensate is trapped in double-well potential. The vortex lattice structure in a rotating triple-well trap potential and its pinning shows very interesting features. We show the existence and pinning of a new type of hidden vortices whose phase profile is similar to that of the visible vortices.

Structure and dynamics of a rotating superfluid Bose-Fermi mixture

“…The three singly quantized phase defects show that the circular density hole is not a giant vortex. Actually, they are known as singly quantized hidden vortices [15,27,33,46] because they carry significant angular momentum, though they are invisible in the in situ density profile of the BEC. Only after including the hidden vortices can the Feynman rule be satisfied [15,47,48].…”

Disorder-induced vortex lattice melting in a Bose-Einstein condensate

“…It may be mentioned here that according to Feynman rule < L z >∼ N/2 where N is the number of vortices in the system. If there are both visible and hidden vortices in the condensate then < L z >∼ (N v +N h )/2 where N v and N h denote the total number of visible and hidden vortices respectively in the system [16]. On careful examination we observed that there are three hidden vortices inside the giant hole.…”

“…The increase in the angular difference |α 1 − α 2 | max show that the vortex lattice gets increasingly distorted with the strength of the impurity potential V 0 (red line). Similarly the impurity potential energy E impurity initially decreases quite rapidly with increasing V 0 (green dots) and finally it attains nearly a constant value showing that the vortex lattice has got pinned to the impurity [16]. It is known that a 'giant hole' created in BEC can be used to study controlled circular superflow and phase slippage in superfluids and also the transverse Tkachenko modes in the vortex lattice [43].…”

“…When the rotating BEC is placed in a co-rotating optical lattice the vortex lattice gets pinned to the optical lattice [15]. Recently, we have shown that the hidden vortices can also be pinned by the optical lattice [16]. The study of melting of vortex lattice in BEC is an important problem as it provide an ideal system for understanding the mechanism of lattice melting of the two-dimensional systems in general.…”

“…The value of the parameter γ has been obtained by fitting theoretical results with experiments to be γ = 0.03 [36]. Thereafter this particular value of the parameter (γ = 0.03) have been used by several authors [16,28,[37][38][39] etc. for studying vortex dynamics in BEC.…”