Crossover from weak to strong quench in a spinor Bose-Einstein condensate

Abstract

We investigate the early-time dynamics of a quasi-two-dimensional spin-1 antiferromagnetic Bose-Einstein condensate after a sudden quench from the easy-plane to the easy-axis polar phase. The post-quench dynamics shows a crossover behavior as the quench strengthq is increased, whereq is defined as the ratio of the initial excitation energy per particle to the characteristic spin interaction energy. For a weak quench, long-wavelength spin excitations are dominantly generated, leading to the formation of irregular spin domains. With increasingq, the length scale of the initial spin excitations decreases, and we demonstrate that the long-wavelength instability is strongly suppressed for a high value ofq > 2. The observed crossover behavior is found to be consistent with the Bogoliubov description of the dynamic instability of the initial spinor condensate.

Quantum Elliptic Vortex in a Nematic-Spin Bose-Einstein Condensate

“…Discussion.-Although the wall-HQV composites were thought to be finally unstable, decaying into conventional axisymmetric vortices due to the snake instability of the wall [39,40], the result suggests that they survive as elliptic vortices after the phase transition. The vortices including their dynamics will be observed through the transverse-spin spots by in situ magnetization imaging [29].…”

“…Accordingly, "HQV-wall plasma" an analog of quarkgluon plasma (QGP), occurs at a finite temperature T at least for T > ðq=k B Þ in nematic-spin BECs, where thermal fluctuations free the spin spots from the confinement by the AF-core soliton. In this sense, the observed phasetransition dynamics [39,40] are regarded as simulations of the transition dynamics from QGP to hadrons like the big bang simulation in "little bang" [80]. Further investigations on the dynamics and interactions of elliptic vortices will shed light on unexplored phase-transition dynamics in different physical systems.…”

“…Here, it is theoretically shown that a wall-HQV composite in spin-1 BECs [39,40] takes an exotic state in equilibrium with a small positive quadratic Zeeman effect. This state, called the elliptic vortex, is hydrodynamically considered the Joukowski transform of a conventional vortex and has an elliptic structure with spin spots (Fig.…”

“…The wall-HQV composites were first realized as the double-core vortices in 3 He-B [31] and revisited [32][33][34], motivated by the early Universe scenario nucleating the composites of the Kibble-Lazarides-Shafi (KLS) walls and cosmic strings [35][36][37]. Recently, the nonequilibrium dynamics of wall-HQV composites were observed in phase transition from the antiferromagnetic (AF) phase to the polar (P) phase [38] in a spin-1 23 Na BEC [39,40].…”

“…, the condensate density is expressed by the dot product [39,40], the ground state is in the P state Φ ¼ Φ P ¼ ½0; 0; ffiffiffiffiffi ffi n P p e iθ G T with the bulk density n P ¼ ðμ=c 0 Þ and the order-parameter phase θ G . By rescaling energy and length by μ and ξ n ≡ ðℏ= ffiffiffiffiffiffiffi Mμ p Þ, respectively, the P phase is parametrized by two dimensionless quantities (c 2 =c 0 ) and (q=μ).…”