Biased dynamics of the miscible-immiscible quantum phase transition in a binary Bose-Einstein condensate

A quantum phase transition from the miscible to the immiscible phase of a quasi-one-dimensional binary Bose-Einstein condensate is driven by ramping down the coupling amplitude of its two hyperfine states. It results in a random pattern of spatial domains where the symmetry is broken separated by defects. In distinction to previous studies [J. Sabbatini et al., Phys. Rev. Lett. 107, 230402 (2011), New J. Phys. 14 095030 (2012)], we include nonzero detuning between the light field and the energy difference of the states, which provides a bias towards one of the states. Using the truncated Wigner method, we test the biased version of the quantum Kibble-Zurek mechanism [M. Rams et al., Phys. Rev. Lett. 123, 130603 (2019)] and observe a crossover to the adiabatic regime when the quench is sufficiently fast to dominate the effect of the bias. We verify a universal power law for the population imbalance in the nonadiabatic regime both at the critical point and by the end of the ramp. Shrinking and annihilation of domains of the unfavourable phase after the ramp, that is, already in the broken symmetry phase, enlarges the defect-free sections by the end of the ramp. The consequences of this phase-ordering effect can be captured by a phenomenological power law.Comment: 11 pages, 7 figures; Updated with changes made for publication in Physical Review

Frequency beating and damping of breathing oscillations of a harmonically trapped one-dimensional quasicondensate

We study the breathing (monopole) oscillations and their damping in a harmonically trapped one-dimensional (1D) Bose gas in the quasicondensate regime using a finite-temperature classical field approach. By characterizing the oscillations via the dynamics of the density profile's rms width over long time, we find that the rms width displays beating of two distinct frequencies. This means that 1D Bose gas oscillates not at a single breathing mode frequency, as found in previous studies, but as a superposition of two distinct breathing modes, one oscillating at frequency close to $\sim\!\sqrt{3}\omega$ and the other at $\sim\!2\omega$, where $\omega$ is the trap frequency. The breathing mode at $\sim\!\sqrt{3}\omega$ dominates the beating at lower temperatures, deep in the quasicondensate regime, and can be attributed to the oscillations of the bulk of the density distribution comprized of particles populating low-lying, highly-occupied states. The breathing mode at $\sim\!2\omega$, on the other hand, dominates the beating at higher temperatures, close to the nearly ideal Bose gas regime, and is attributed to the oscillations of the tails of the density distribution comprized of thermal particles in higher energy states. The two breathing modes have distinct damping rates, with the damping rate of the bulk component being an order of magnitude larger than that of the tails component, and at least 2--3 times smaller than the damping rate predicted by Landau's theory of damping in 1D.Comment: 11 pages, 8 figure