Nguyen Thanh Phuc, Yuki Kawaguchi, Masahito Ueda
The Bogoliubov theory has proven to be an accurate and versatile tool in the study of weakly- interacting dilute Bose gases at low temperatures, yet there is one exception where it goes qualita- tively wrong, i.e., near the first-order quantum phase transitions. By examining a phase transition in spinor Bose-Einstein condensates (BECs), we find that the energy spectrum given by the Bogoli- ubov theory is inconsistent with the fact that the phase transition is first order. We resolve this problem by calculating the spectrum based on the spinor version of the Beliaev theory. We also discuss the ground-state phase diagram of spin-2 BECs which is modified by quantum fluctuations and the possibility of macroscopic quantum tunneling near the cyclic-nematic phase boundary.
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http://arxiv.org/abs/1301.3642
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