We have observed the persistent flow of Bose-condensed atoms in a toroidal trap. The flow persists without decay for up to 10 s, limited only by experimental factors such as drift and trap lifetime. The quantized rotation was initiated by transferring one unit of the orbital angular momentum from Laguerre-Gaussian photons to each atom. Stable flow was only possible when the trap was multiply connected, and was observed with a Bose-Einstein condensate fraction as small as 20%. We also created flow with two units of angular momentum and observed its splitting into two singly charged vortices when the trap geometry was changed from multiply to simply connected.

We demonstrate the coherent transfer of the orbital angular momentum of a photon to an atom in quantized units of , using a 2-photon stimulated Raman process with Laguerre-Gaussian beams to generate an atomic vortex state in a Bose-Einstein condensate of sodium atoms. We show that the process is coherent by creating superpositions of different vortex states, where the relative phase between the states is determined by the relative phases of the optical fields. Furthermore, we create vortices of charge 2 by transferring to each atom the orbital angular momentum of two photons.

Loading only single atoms into an optical trap with an efficiency in excess of 80% has now been achieved by manipulating the collisions between pairs of atoms. Such a process has previously been limited to about 50% efficiency. The technique will aid the development of neutral-atom-based quantum logic gates. Neutral atoms stored in optical traps are strong candidates for a physical realization of a quantum logic device1,2. Far off-resonance optical traps provide conservative potentials and excellent isolation from the environment, and they may be arranged to produce arbitrary arrays of traps, where each trap is occupied by a single atom that can be individually addressed3,4,5,6. At present, significant effort is being expended on developing two-qubit gates based on coupling individual Rydberg atoms in adjacent optical microtraps7,8,9. A major challenge associated with this approach is the reliable generation of single-atom occupancy in each trap, as the loading efficiency in the past experiments has been limited to 50% (refs 4, 7, 8, 10, 11, 12). Here we report a loading efficiency of 82.7% in an optical microtrap. We achieve this by manipulating the collisions between pairs of trapped atoms through tailored optical fields and directly observing the resulting single atoms in the trap.

We have observed high-order quantum resonances in a realization of the quantum -kicked rotor, using Bose-condensed Na atoms subjected to a pulsed standing wave of laser light. These resonances occur for pulse intervals that are rational fractions of the Talbot time, and are characterized by ballistic momentum transfer to the atoms. The condensate’s narrow momentum distribution not only permits the observation of the quantum resonances at and of the Talbot time, but also allows us to study scaling laws for the resonance width in quasimomentum and pulse interval.

We investigate the dephasing of ultra cold ${}^{85}\mathrm{R}\mathrm{b}$ atoms trapped in an optical dipole trap and prepared in a coherent superposition of their two hyperfine ground states by interaction with a microwave pulse. We demonstrate that the dephasing, measured as the Ramsey fringe contrast, can be reversed by stimulating a coherence echo with a $\pi$ pulse between the two $\frac{\pi }{2}$ pulses, in analogy to the photon echo. We also demonstrate that “echo spectroscopy” can be used to study the quantum dynamics in the trap even when more than ${10}^6$ states are thermally populated and to study the crossover from quantum to classical dynamics.

We report on numerical and experimental observations of islands of stability induced in a Bunimovich stadium atom-optics billiard by a soft wall repulsive potential. A deviation from exponential decay of the survival probability of atoms in an open billiard is observed, and explained by the presence of these stable islands and a sticky region surrounding them. We also investigate islands in dispersing billiards with soft walls, and predict a new mechanism for their formation.