Characterisation of a three-dimensional Brownian motor in optical lattices

Abstract

We present here a detailed study of the behaviour of a three dimensional Brownian motor based on cold atoms in a double optical lattice [P. Sjölund et al., Phys. Rev. Lett. 96, 190602 (2006)]. This includes both experiments and numerical simulations of a Brownian particle. The potentials used are spatially and temporally symmetric, but combined spatiotemporal symmetry is broken by phase shifts and asymmetric transfer rates between potentials. The diffusion of atoms in the optical lattices is rectified and controlled both in direction and speed along three dimensions. We explore a large range of experimental parameters, where irradiances and detunings of the optical lattice lights are varied within the dissipative regime. Induced drift velocities in the order of one atomic recoil velocity have been achieved.PACS. 32.80.Lg Mechanical effects of light on atoms, molecules, and ions -05.40.Jc Brownian motion -32.80.Pj Optical cooling of atoms; trapping arXiv:0704.3955v1 [physics.atom-ph]

Assessment of a time-of-flight detection technique for measuring small velocities of cold atoms

“…The uncertainty in the initial velocity of the center of mass of the atomic cloud is satisfyingly low, compared to typical velocities induced by our BM, 9 which are of the order of 1 mm/s. Also, the uncertainty in the temperature is low compared to the temperature shifts in interest in most measurements.…”

“…The atoms trapped in an optical lattice have indeed been shown to reach a steady state velocity rather fast. 9 By summing the systematic errors, a combined systematic uncertainty for the most commonly extracted entities from the TOF signal can be obtained. These have been summarized in Table I.…”

“…The single optical lattice is used to study, i.e., the shape of the velocity distribution 12 and the time evolution of cooling processes. 13 The double optical lattices have a controllable relative spatial phase and are therefore used for, e.g., the realization of a three-dimensional ͑3D͒ controllable BM, 8,9 where the phase is used to control the size and direction of the induced drift. The controllable phase also opens the possibilities for experiments with cold collisions, 22 quantum gate operations, 23 and realizations of a quantum random walk.…”

Fluctuation-induced drift in a gravitationally tilted optical lattice

“…The experimental set-up has been described in more detail elsewhere [18,19,31,32]. In short, we trap and cool cesium atoms with standard laser cooling techniques [21].…”

Breaking the symmetry of a Brownian motor with symmetric potentials

“…Such a Brownian motor, where the asymmetry is given by a combination of a non-zero relative spatial phase and unequal transfer rates between only two symmetric, periodic potentials, has been demonstrated both numerically [17] and experimentally [18,19,20], including with real-time control of the drift [21]. The original idea of using two phase-shifted symmetric potentials [17] (along with its implementation [18,19,20,21]) was based on laser-cooled atoms interacting with two optical lattices, created from the interference of laser beams [22]. As such, it was assumed that the asymmetry coming from unequal transfer rates between the two phase-shifted optical lattices, as occurs "naturally" in the system, was the asymmetry driving the Brownian motor [17].…”