Experimental investigation of early-time diffusion in the quantum kicked rotor using a Bose-Einstein condensate

We report the experimental observation of resonances in the early-time momentum diffusion rates for the atom-optical delta-kicked rotor. In this work a Bose-Einstein condensate provides a source of ultra-cold atoms with an ultra-narow initial momentum distribution, which is then subjected to periodic pulses (or "kicks") using an intense far-detuned optical standing wave. A quantum resonance occurs when the momentum eigenstates accumulate the same phase between kicks leading to ballistic energy growth. Conversely, an anti-resonance is observed when the phase accumulated from successive kicks cancels and the system returns to its initial state. Our experimental results are compared with theoretical predictions.