Phase structure and low-energy excitations in spinor Bose-Einstein condensates

E. Y. Vedmedenko, M Schult, Jochen Kronjäger +3 more

We elucidate dipolar magnetic interaction effects in spinor condensates at a low-background field. In particular, we show that arrays of ferromagnetic spinor Bose–Einstein condensates show a rich phase structure that is strongly influenced by the competition of shape anisotropy and higher-order magnetostatic contributions both depending on the condensate's form.

Wai-ho Tang

Shohei Watabe, Yusuke S. Kato, Yoji Ohashi

We investigate tunneling properties of collective modes in the polar phase of a spin-1 spinor Bose-Einstein condensate (BEC). This spinor BEC state has two kinds of gapless modes (i.e., Bogoliubov and spin-wave). Within the framework of mean-field theory at $T=0$, we show that these Goldstone modes exhibit perfect transmission in the low-energy limit. Their anomalous tunneling behavior still holds in the presence of superflow, except in the critical current state. In the critical current state, while the tunneling of Bogoliubov mode is accompanied by finite reflection, the spin wave still exhibits perfect transmission, unless the strengths of spin-dependent and spin-independent interactions take the same value. We discuss the relation between perfect transmission of a spin wave and underlying superfluidity through a comparison of wave functions of the spin wave and the condensate.

Dan Stamper-Kurn

G. Edward Marti, Ryan Olf, Sean Lourette +2 more

D. Baillie, P. B. Blakie

We develop a general theory of spin-dependent Bragg spectroscopy for spinor Bose-Einstein condensates. This spectroscopy involves using a density and spin-coupled optical probe to excite the system. We show that within the linear-response regime the momentum or energy transferred by the probe is determined by a set of density and spin-density dynamic structure factors. We derive a set of $f$-sum rules that provides rigorous constraints for the first energy moments of these structure factors. As an application we compute the dynamic structure factors for cases within all four distinct phases of a spin-1 condensate using Bogoliubov theory. Our results demonstrate that spin-dependent Bragg spectroscopy can be used to selectively investigate the various phonon and magnon excitation branches and will be a useful tool for advancing our understanding of spinor condensates.