R. M. Godun

Dynamic manipulation of Bose-Einstein condensates with a spatial light modulator

We manipulate a Bose-Einstein condensate using the optical trap created by the diffraction of a laser beam on a fast ferroelectric liquid crystal spatial light modulator. The modulator acts as a phase grating which can generate arbitrary diffraction patterns and be rapidly reconfigured at rates up to 1 kHz to create smooth, time-varying optical potentials. The flexibility of the device is demonstrated with our experimental results for splitting a Bose-Einstein condensate and independently transporting the separate parts of the atomic cloud.

Signatures of quantum stability in a classically chaotic system

We experimentally and numerically investigate the quantum accelerator mode dynamics of an atom optical realization of the quantum delta-kicked accelerator, whose classical dynamics are chaotic. Using a Ramsey-type experiment, we observe interference, demonstrating that quantum accelerator modes are formed coherently. We construct a link between the behavior of the evolutions fidelity and the phase space structure of a recently proposed pseudoclassical map, and thus account for the observed interference visibilities.

Collisional relaxation of Feshbach molecules and three-body recombination in 87Rb Bose-Einstein condensates

We predict the resonance-enhanced magnetic field dependence of atom-dimer relaxation and three-body recombination rates in a {sup 87}Rb Bose-Einstein condensate close to 1007 G. Our exact treatments of three-particle scattering explicitly include the dependence of the interactions on the atomic Zeeman levels. The Feshbach resonance distorts the entire diatomic energy spectrum, causing interferences in both loss phenomena. Our two independent experiments confirm the predicted recombination loss over a range of rate constants that spans four orders of magnitude.

Accelerator-mode-based technique for studying quantum chaos

We experimentally demonstrate a method for selecting small regions of phase space for kicked rotor quantum chaos experiments with cold atoms. Our technique uses quantum accelerator modes to selectively accelerate atomic wave packets with localized spatial and momentum distributions. The potential used to create the accelerator mode and subsequently realize the kicked rotor system is formed by a set of off-resonant standing-wave light pulses. We also propose a method for testing whether a selected region of phase space exhibits chaotic or regular behavior using a Ramsey type separated field experiment.

A method of state-selective transfer of atoms between microtraps based on the Franck-Condon principle

We present a method of transferring a cold atom between spatially separated microtraps by means of a Raman transition between the ground motional states of the two traps. The intermediate states for the Raman transition are the vibrational levels of a third microtrap, and we determine the experimental conditions for which the overlap of the wavefunctions leads to an efficient transfer. There is a close analogy with the Franck–Condon principle in the spectroscopy of molecules. The spin-dependent manipulation of neutral atoms in microtraps has important applications in quantum information processing. We also show that, starting with several atoms, precisely one atom can be transferred to the final potential well hence giving deterministic preparation of single atoms.

How dark is a grey state

We present experimental results showing that a dark state with finite lifetime, a grey state, becomes darker the more the atom is exposed to on-resonant light. We discuss this phenomenon theoretically in the context of the complex eigenenergies and show that it can be understood qualitatively in terms of the quantum Zeno effect. The predicted dependence of the lifetime on the composition of the grey state and on the light intensity is experimentally confirmed with caesium atoms. This has implications for velocity-selective coherent population trapping and adiabatic transfer.

An Atom Interferometer as a Thermometer

Atom interferometers provide a unique way in which to study atomic de Broglie waves1} and properties of atomic sources. One such property of the atomic ensemble, the temperature, is associated with the coherence length, which can be measured with an interferometer. This can be used to deduce the temperature even at very low temperatures where time of flight methods fail.

Limits of the separated-path Ramsey atom interferometer

We describe in detail our caesium atom interferometer which uses a combination of microwaves and momentum-changing adiabatic transfer pulses. This combination allows us to achieve spatial separation between the arms of the interferometer. We account for the observed visibility of the resulting interference fringes and find that the effects which contribute the most are optical pumping and magnetic fields.