28aXB-7 Bose 凝縮体における渦糸状態の集団励起と Beliaev 減衰

Rukuan Wu, Zhaoxin Liang

Beliaev damping provides a fundamental mechanism for dissipation of quasiparticles. Previous research has shown that the two-component internal degrees of freedom has no nontrivial effect on Beliaev damping. Here we provide the first example where the spinor nature of Bose gases can manifest itself in the Beliaev damping by way of spin-obit coupling. We identify novel features of the Beliaev decay rate due to spin-orbit coupling; in particular, it shows an explicit dependence on the spin-density interaction and diverges at the interaction-modified phase boundary between the zero-momentum and plane wave phases. This represents a manifestation of the effect of spin-orbit coupling in the beyond-mean-field regime, which by breaking Galilean invariance couples excitations in the density and spin channels. We further show that the measurement of the Beliaev damping rate is experimentally feasible through the measurement of spin polarizability susceptibility, which has been already achieved in spin-orbit-coupled Bose gases.

雅彦 奥村, 由也 山中

Isara Chantesana, Orioli Asier Pineiro, G Schmalz Thomas

Shai Ronen

The well-known Bogoliubov expression for the spectrum of a weakly interacting dilute Bose gas becomes inadequate when the density or interactions strength are increased. The corrections to the spectrum due to stronger interactions were first considered by Beliaev (S. T. Beliaev, Sov. Phys.-JETP, 7:289, (1958)). We revisit Beliaev's theory and consider its application to a dilute gas with van der Waals interactions, where the scattering length may be tuned via a Fano-Feshbach resonance. We numerically evaluate Beliaev's expression for the excitation spectrum in the intermediate momentum regime, and we also examine the consequences of the momentum dependence of the two-body scattering amplitude.These results are relevant to the interpretation of a recent Bragg spectroscopy experiment of a strongly interacting Bose gas.

昌平 渡部

E. Hodby, Onofrio M. Maragò, Gerald Hechenblaikner +1 more

We report the first experimental observation of Beliaev coupling between collective excitations of a Bose-Einstein condensed gas. Beliaev coupling is not predicted by the Gross-Pitaevskii equation and so this experiment tests condensate theory beyond the mean field approximation. Measurements of the amplitude of a high frequency scissors mode show that the Beliaev process transfers energy to a lower-lying mode and then back and forth between these modes, unlike Landau processes which lead to a monotonic decrease in amplitude. To enhance the Beliaev process we adjusted the geometry of the magnetic trapping potential to give a frequency ratio of 2 to 1 between the two scissors modes.