Two identical finite quantum systems prepared initially at different temperatures, isolated from the environment, and subsequently brought into contact are demonstrated to relax towards Gibbs-like quasiequilibrium states with a common temperature and small fluctuations around the time-averaged expectation values of generic observables. The temporal thermalization process proceeds via a chain of intermediate Gibbs-like states. We specify the conditions under which this scenario occurs and corroborate the quantum equilibration with two different models.

We devise a microscopic model for the emergence of a collision-induced, fermionic atomic current across a tilted optical lattice. Tuning the--experimentally controllable--parameters of the microscopic dynamics allows us to switch from Ohmic to negative differential conductance.

We invent an ac-driven quantum motor consisting of two different, interacting ultracold atoms placed into a ring-shaped optical lattice and submerged in a pulsating magnetic field. While the first atom carries a current, the second one serves as a quantum starter. For fixed zero-momentum initial conditions the asymptotic carrier velocity converges to a unique non-zero value. We also demonstrate that this quantum motor performs work against a constant load.PACS numbers: 37.10.Jk,84.50.+d Linear or rotational motion presents the basic working principle powering all sorts of machines. For nearly two centuries, since the invention of the first electrical motor [1], the ever continuing miniaturization of devices has profound consequences for several branches of science, industry, and everyday life. This process has already passed the scale of micrometers [2] and has entered the realm of the world of nanoscale [3]. Bioinspired devices such as chemical or light driven synthetic molecular motors identify just one of those recent successes [4]. While the operational description of such molecular motors mainly rests on classical concepts, much less is known for operational schemes that are fully quantum mechanical in nature. An ideal resource for the latter possibility is the dynamics of cold atoms that are positioned in optical potentials [5].With this work, we put forward a setup for a quantum motor which consists of two species of interacting, distinguishable quantum particles that are loaded into a ring-shaped optical potential. The blueprint for such an underlying ring-shaped one-dimensional optical lattice has been proposed recently [6] and a first experimental realization has been reported in [7]. Here, we employ this setup to devise an engine which works as a genuine ac-driven quantum motor.ac-quantum motor.- Figure 1 outlines our device. The ring-shaped optical potential, which results either from the interference of a Laguerre-Gauss (LG) laser beam with a plane wave [6] or, alternatively, of two collinear LG beams with different frequencies [7] is capable of trapping two interacting atoms. One of the atoms, termed "carrier", c, is driven by an external field, while the other atom, termed "starter", s, interacts locally via elastic swave collisions with the "carrier", but remains unaffected by the driving field [8]. Two possible setups that come to mind are (i) A neutral "starter" and an ionized "carrier", a suitable driving field can be implemented in a way typically done for electrons placed in a conducting ring, i.e., by a time-dependent magnetic flux threading the lattice [9]. (ii) A spinless "starter" and a "carrier"-atom with a non-zero spin which is driven by a time-dependent coneshaped magnetic field of an Ioffe-Pritchard trap [6,10].We next assume that both atoms are loaded into the The ac-driven, total Hamiltonian H tot of the motoris composed of the time-dependent Hamiltonian H c (t) for the "carrier"and for the "starter" H s , respectively, i.e.,Here, J c and J s are the corresponding hopping str...

The paper studies Bloch oscillations of cold neutral atoms in the optical lattice. The effect of spontaneous emission on the dynamics of the system is analyzed both analytically and numerically. The spontaneous emission is shown to cause (i) the decay of Bloch oscillations with the decrement given by the rate of spontaneous emission and (ii) the diffusive spreading of the atoms with a diffusion coefficient depending on both the rate of spontaneous emission and the Bloch frequency.