Superfluid toroidal currents in atomic condensates

The spectrum of collective excitations of oblate toroidal condensates within the Bogoliubov approximation was studied, and the dynamical stability of ring currents around the torus explored. The transition from spheroidal to toroidal geometry of the trap displaced the energy levels into narrow bands. A simple, but accurate, formula was detailed for the lowest angular acoustic modes of excitation, and the splitting energy when a background current is present.

Microcontroller based double beam modulation system for atomic scattering experiments

Double beam modulation is widely used in atomic collision experiments in the case where the noise arising froth each of the beams exceeds the measured signal. A method for minimizing the statistical uncertainty in a measured signal in a given time period is discussed, and a flexible modulation and counting system based on a low cost PIC microcontroller is described. This device is capable of modifying the acquisition parameters in real time during the course of an experimental run. It is shown that typical savings in data acquisition time of approximately 30% can be achieved using this optimized modulation scheme.

Observing time-dependent vibrational quantum dynamics in deuterium hydride molecular ions

Few-cycle laser pulses are used to "pump and probe" image the vibrational wavepacket dynamics of a HD+ molecular ion. The quantum dephasing and revival structure of the wavepacket are mapped experimentally with time-resolved photodissociation imaging. The motion of the molecule is simulated using a quantum-mechanical model predicting the observed structure. The coherence of the wavepacket is controlled by varying the duration of the intense laser pulses. By means of a Fourier transform analysis both the periodicity and relative population of the vibrational states of the excited molecular ion have been characterized.

Isolated vibrational wavepackets in D-2(+): Defining superposition conditions and wavepacket distinguishability

Tunnel ionization of room-temperature D-2 in an ultrashort (12 femtosecond) near infrared (800 nm) pump laser pulse excites a vibrational wavepacket in the D-2(+) ions; a rotational wavepacket is also excited in residual D-2 molecules. Both wavepacket types are collapsed a variable time later by an ultrashort probe pulse. We isolate the vibrational wavepacket and quantify its evolution dynamics through theoretical comparison. Requirements for quantum computation (initial coherence and quantum state retrieval) are studied using this well-defined (small number of initial states at room temperature, initial wavepacket spatially localized) single-electron molecular prototype by temporally stretching the pump and probe pulses.

Reconstruction of atomic ionization probabilities in intense laser fields

Application of a parallel-projection inversion technique to z-scan spectra of multiply charged xenon and krypton ions, obtained by non-resonant field ionization of neutral targets, has for the first time permitted the direct observation of intensity-dependent ionization probabilities. These ionization efficiency curves have highlighted the presence of structure in the tunnelling regime, previously unobserved under full-volume techniques.

Atomic and molecular ions in intense ultra-fast laser fields

The interaction of a 60 fs 790 nm laser pulse with beams of Ar+, C+, H2+, HD+ and D2+ are discussed. Intensities up to 10^16 Wcm-2 are employed. An experimental z-scanning technique is used to resolve the intensity dependent processes in the confocal volume.