Abstract
The phenomenon of metastability can shape dynamical processes on all temporal and spatial scales. Here, we induce metastable dynamics by pumping ultracold bosonic atoms from the lowest band of an optical lattice to an excitation band, via a sudden quench of the unit cell. The subsequent relaxation process to the lowest band displays a sequence of stages, which include a metastable stage, during which the atom loss from the excitation band is strongly suppressed. Using classical-field simulations and analytical arguments, we provide an explanation for this experimental observation, in which we show that the transient condensed state of the atoms in the excitation band is a dark state with regard to collisional decay and tunneling to a low-energy orbital. Therefore the metastable state is stabilized by destructive interference due to the chiral phase pattern of the condensed state. Our experimental and theoretical study provides a detailed understanding of the different stages of a paradigmatic example of many-body relaxation dynamics.
Highlights
The relaxation dynamics of a many-body system that has been driven out of equilibrium can either be governed by a single time scale, as in an exponential decay process, or take a more intricate form [1]
Using classical-field simulations and analytical arguments, we provide an explanation for this experimental observation, in which we show that the transient condensed state of the atoms in the excitation band is a dark state with regard to collisional decay and tunneling to a low-energy orbital
By measuring the momentum resolved occupation of the bands via band mapping, we have observed three stages of dynamics, which are the relaxation dynamics to the metastable state, the metastable state itself and the relaxation to the thermal equilibrium state. Utilizing both numerical and analytical reasoning, we have provided an interpretation of this dynamical process
Summary
The relaxation dynamics of a many-body system that has been driven out of equilibrium can either be governed by a single time scale, as in an exponential decay process, or take a more intricate form [1]. In this work we present an experimental and theoretical study of metastable dynamics of ultracold atoms in the second band of an optical lattice. Our experiments begin with the preparation of an ultracold gas of bosonic atoms in the ground state of an optical lattice This lattice is composed of shallow and deep potential wells, forming a checkerboard pattern in the xy plane, see Fig. 1(a). By combining the results of our numerical simulations with analytical arguments we identify the origin of the observed metastability as destructive interference This interference effect arises due to the chiral phase texture of the condensate. As a consequence of these interference mechanisms, the condensate with respect to collisions constitutes a many-body dark state and direct relaxation of the coherent metastable state to the thermal ground state is inhibited, see Fig. 2.
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