Classical ratchet potentials, which alternate a driving potential with periodic random dissipative motion, can account for the operation of biological motors. We demonstrate the operation of a quantum ratchet, which differs from classical ratchets in that dissipative processes are absent within the observation time of the system (Hamiltonian regime). An atomic rubidium Bose-Einstein condensate is exposed to a sawtooth-like optical lattice potential, whose amplitude is periodically modulated in time. The ratchet transport arises from broken spatiotemporal symmetries of the driven potential, resulting in a desymmetrization of transporting eigenstates (Floquet states). The full quantum character of the ratchet transport was demonstrated by the measured atomic current oscillating around a nonzero stationary value at longer observation times, resonances occurring at positions determined by the photon recoil, and dependence of the transport current on the initial phase of the driving potential.
We report on the successful experimental realization of a quantum ratchet for ultracold atoms in a driven spatially asymmetric optical lattice. Ratchets are usually considered as a tool, which rectify an otherwise undirected, for instance oscillating or fluctuating, motion of particles or objects. In order to observe a directed transport of atoms one has to break the space-time symmetry of the system [1][2][3]. Here, we report on the realization of a quantum ratchet in the absence of dissipative processes (Hamiltonian regime) within the interaction time. 0.2 -se :$ -----E 0 ::J C (1) E 0 E -0.2 o 50 modulation period 100 Fig. 1 Time evolution ofthe mean momentum for different values of the temporal phase: (a) e= n/2 (triangles) , (b) e= -n/2 (circles) and (c) e= n (squares) . The oscillation of the current is attributed to interference effects between Floquet eigenstates. The solid lines are splines to guide the eye.In our experiment, we produce a Bose-Einstein condensate of 87Rb atoms in an optical dipole trap with about 5 x 10 4 atoms. The ratchet is built using a combined A/2 and A/4 periodic optical lattice, which is modulated in time. The A/2 lattice is generated by the usual standing wave method and the A/4 lattice is achieved within a scheme of stimulated Raman transitions. A detailed description of the experimental setup was given in previous works, see for example [4,5]. The effective potential for the BEe can be written as Vratchet(X,t) = V(x) ·E(t), where the spatial modulation is V (x) = VIcos 2 (kx) +V2 cos 2 (2kx +q,/ 2) and the temporal modulation of the amplitude is E(t) = EI cos 2 ( rot/ 2) +E2cos? (rot + e/ 2). We have studied the time evolution of the ratchet system after a variable number of lattice modulation cycles. Typical results of our measurements are shown in Fig. 1 for different symmetry situations. Different eigenvalues of the corresponding Floquet matrix overlap, leading to an oscillatory behavior of the current. This phenomenon does not appear in a classical ratchet and can only be explained by quantum mechanics. References[I] S. Denisov, L. Morales-Molina , S. Flach . and P. Hanggi, "Periodically driven quantum ratchets : Symmetries and resonance s," Phys. Rev. A 75, 063424 (2007) [2] R Gommers, S. Bergamini, and F. Renzoni , "Dis sipation-Induced Symmetry Breaking in a Driven Optical Lattice ," Phys. Rev. Lett. 95, 073003 (2005) [3] RD. Astumian, "Thermodynamics and Kinetics of a Brownian Motor," Science 276, 917 (1997) [4] G. Ritt, C. Geckeler, T. Salger, G. Cennini , and M. Weitz, "Fourier synthesis of optical potentials for atomic quantum gases," Phys. Rev. A 74, 063622 (2006) [5] T.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.