Abstract
The ratchet phenomenon is a means to get directed transport without net forces. Originally conceived to rectify stochastic motion and describe operational principles of biological motors, the ratchet effect can be used to achieve controllable coherent quantum transport. This transport is an ingredient of several perspective quantum devices including atomic chips. Here we examine coherent transport of ultra-cold atoms in a rocking quantum ratchet. This is realized by loading a rubidium atomic Bose–Einstein condensate into a periodic optical potential subjected to a biharmonic temporal drive. The achieved long-time coherence allows us to resolve resonance enhancement of the atom transport induced by avoided crossings in the Floquet spectrum of the system. By tuning the strength of the temporal modulations, we observe a bifurcation of a single resonance into a doublet. Our measurements reveal the role of interactions among Floquet eigenstates for quantum ratchet transport.
Highlights
The ratchet phenomenon is a means to get directed transport without net forces
We demonstrate the control of coherent quantum transport in a rocking quantum ratchet by engineering avoided crossings between Floquet states
Modulated optical potentials can be put to work as tunable quantum ‘metamaterials’
Summary
Conceived to rectify stochastic motion and describe operational principles of biological motors, the ratchet effect can be used to achieve controllable coherent quantum transport. We examine coherent transport of ultra-cold atoms in a rocking quantum ratchet This is realized by loading a rubidium atomic Bose–Einstein condensate into a periodic optical potential subjected to a biharmonic temporal drive. Physical intuition may sometimes apply, for example, a high velocity can be expected in the case of resonant driving, when the modulating frequency matches the characteristic frequency of the potential, as was verified with experiments using cold atoms in the regime of classical ratchets[22,23,24] and, as well, with a flashing quantum ratchet realized with a Bose–Einstein condensate of rubidium atoms[11]
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