Bloch Oscillations of Bosonic Lattice Polarons

December 9, 2014
Figure 1

Copyright 2014 by the American Physical Society

Figure 1: (a) An impurity (blue) is immersed in a homogeneous 3D BEC (red) and constrained to the lowest band of a 1D optical lattice. Strong interactions with the Bose gas lead to polaron formation and a modified dispersion. [From F. Grusdt, A. Shashi, D. Abanin, and E. Demler, "Bloch oscillations of bosonic lattice polarons," Phys. Rev. A 90, 063610 (4 Dec 2014), http://dx.doi.org/10.1103/PhysRevA.90.063610]

A recent 'Editor's Suggested' article in Physical Review A is by members of Demler's research group Fabian Grusdt, Aditya Shashi, and Dmitry Abanin (see the citation, above). Together with Prof. Eugene Demler, they consider a single-impurity atom confined to an optical lattice and immersed in a homogeneous Bose-Einstein condensate (BEC). Interaction of the impurity with the phonon modes of the BEC leads to the formation of a stable quasiparticle, the polaron. The physicists use a variational mean-field approach to study dispersion renormalization and derive equations describing nonequilibrium dynamics of polarons by projecting equations of motion into mean-field-type wave functions.

As a concrete example, they apply their method to study dynamics of impurity atoms in response to a suddenly applied force and explore the interplay of coherent Bloch oscillations and incoherent drift. They obtain a nonlinear dependence of the drift velocity on the applied force, including a sub-Ohmic dependence for small forces for dimensionality d > 1 of the BEC. For the case of heavy impurity atoms, the scientists derive a closed analytical expression for the drift velocity. The results show considerable differences with the commonly used phenomenological Esaki-Tsu model.