Observation of high-order quantum resonances in the kicked rotor

Quantum resonances in the kicked rotor are characterized by a dramatically increased energy absorption rate, in stark contrast to the momentum localization generally observed. These resonances occur when the scaled Planck's constant h=r/s4 pi, for any integers r and s. However, only the h=r2 pi resonances are easily observable. We have observed high-order quantum resonances (s > 2) utilizing a sample of low energy, noncondensed atoms and a pulsed optical standing wave. Resonances are observed for h=r/164 pi for integers r=2-6. Quantum numerical simulations suggest that our observation of high-order resonances indicate a larger coherence length (i.e., coherence between different wells) than expected from an initially thermal atomic sample.