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˜ = r s · 4π, for any integers r and s. However only the˜ = r · 2π resonances are easily observable. We have observed high-order quantum resonances (s > 2) utilizing a sample of low temperature, non-condensed atoms and a pulsed optical standing wave. Resonances are observed for˜ = r 16 · 4π for integers r = 2 − 6. Quantum numerical simulations suggest that our observation of high-order resonances indicates a larger coherence length than expected from an initially thermal atomic sample.PACS numbers: 05.45. Mt, 32.80.Pj, 32.80.Lg A rotor subjected to a periodically pulsed sinusoidal potential ("kicked rotor") is one of the most widely studied paradigms of chaotic dynamics. Ever since the qualitative differences between the classical kicked rotor and the quantum kicked rotor (QKR) became evident [1], the QKR has proven to be a rich system for studying quantum-classical correspondence, decoherence, and quantum dynamics in general. To this day the study of the standard QKR as well as alternative kicked rotor Hamiltonians [2,3] is an actively pursued field. Much of the early work was done through theoretical and numerical analysis, with one of the more important discoveries being the realization that momentum localization in the QKR can be thought of as a form of Anderson localization [4]. An experimental breakthrough in the field came when laser cooling and optical trapping of atoms allowed the use of optical lattices as a linear momentum analogue of the QKR. This led to the observation of some of the theoretical predictions such as momentum localization [5] as well as studies of decoherence [6] and interesting results arising from modifications to the Hamiltonian of the QKR [7,8].Quantum resonances [5,9] are another aspect of the QKR which have been of experimental interest recently: for certain parameters, heating is greatly enhanced in contrast to the momentum localization usually present in the quantum kicked rotor. In the presence of gravity or other linear potentials one sees accelerator modes[10], similar to quantum resonances except that there is an increase in average momentum as well as momentum spread. Like other aspects of the quantum kicked rotor, quantum resonances are useful for studying quantumclassical correspondence. Work has gone into studying the effect in the presence of noise and the competition with momentum localization and the resonances [11].Here we present experimental observation of quantum resonances utilizing a sample of cold thermal rubidium atoms in an optical lattice. Specifically, we report our observation of high-order quantum resonances. There have been studies of high-order accelerator modes previously [12] as well as a concurrent observation of highorder resonances in a Bose-Einstein condensate [13]. In all previous experiments with nondegenerate at...

The bichromatic force has been used to both slow and collimate a beam of metastable 2(3)S He atoms (He*). The collimation capture range is an extraordinary +/-85 m/s corresponding to approximately 0.18 radians from our source. Both slowing and collimation were accomplished in the unprecedented short distance of approximately 5 cm each. The overall brightness increase is x3200, and there is potential for considerably more.

We measure the application of simple and compound pulses consisting of time-dependent spatial translations to coupling vibrational states of ultracold 85 Rb atoms in a far-detuned 1D optical lattice. The lattice wells are so shallow as to support only two bound states, and we prepare the atoms in the ground state. The lattice is oriented vertically, leading to a tilted-washboard potential analogous to those encountered in condensed-matter systems. Experimentally, we find that a square pulse consisting of lattice displacements and a delay is more efficient than single-step and Gaussian pulses. This is described as an example of coherent control. It is striking that contrary to the intuition that soft pulses minimize loss, the Gaussian pulse is outperformed by the square pulse. Numerical calculations are in strong agreement with our experimental results and show the superiority of the square pulse to the single-step pulse for all lattice depths and to the Gaussian pulse for lattice depths greater than 7 lattice recoil energies. We also compare the effectiveness of these pulses for reviving oscillations of atoms in vibrational superposition states using the pulse-echo technique. We find that the square and Gaussian pulses result in higher echo amplitudes than the single-step pulse. These improved echo pulses allow us to probe coherence at longer times than in the past, measuring a plateau which has yet to be explained. In addition, we show numerically that the vibrational state coupling due to such lattice manipulations is more efficient in shallow lattices than in deep lattices. The coupling probability for an optimized single-step pulse approaches 1/e as the depth goes to infinity (harmonic-oscillator limit), while in shallow lattices with large anharmonicity, the coupling probability reaches a maximum value of 0.51 for a lattice depth of 5 recoil energies. For square and Gaussian pulses the coupling in the lattice is even stronger, reaching maxima of 0.64 at 6 recoil energies and 0.67 at 5 recoil energies, respectively.

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