Shuai Chen, Jin-Yi Zhang, Si-Cong Ji, Zhu Chen, Long Zhang, Zhi-Dong Du, Youjin Deng, Hui Zhai, Jian-Wei Pan
Interaction between matter field and gauge field plays a fundamental role in
many areas of physics. Recently, a non-abelian gauge field has been
successfully synthesized in laboratory for ultracold neutral bosonic atoms,
yielding the coupling between the pseudo-spin of an atom and its orbital
motion. This new superfluid has many unconventional properties remaining to be
explored. Here we study the collective oscillation of a spin-orbit coupled
Bose-Einstein condensate in a harmonic trap. We find that the frequency of
dipole oscillation deviates from the harmonic trap frequency and depends on the
oscillation amplitude. Such an unharmonic behavior reveals the non-abelain
character of the gauge field. We also observe that a magnetization oscillation
is induced by the dipole motion, as a manifestation of the absence of the
Galilean invariance of this system. We develop a variational wave-function
method that well describes the dipole oscillation, except in the regime with
two degenerate single-particle energy minima separated by a low barrier. In
this regime, since the harmonic trapping potential plays an analogous role as
kinetic energy in a real-space double-well potential, macroscopic quantum
tunneling in momentum space is observed in the dipole oscillation.
View original:
http://arxiv.org/abs/1201.6018
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