Andrew C. Wilson

Imaging of s and d partial-wave interference in quantum scattering of identical bosonic atoms

We report on the direct imaging of s and d partial-wave interference in cold collisions of atoms. Two ultracold clouds of 87Rb atoms were accelerated by magnetic fields to collide at energies near a d-wave shape resonance. The resulting halos of scattered particles were imaged using laser absorption. By scanning across the resonance we observed a marked evolution of the scattering patterns due to the energy dependent phase shifts for the interfering s and d waves. Since only two partial-wave states are involved in the collision process the scattering yield and angular distributions have a simple interpretation in terms of a theoretical model.

Periodically locked continuous-wave cavity ringdown spectroscopy

We demonstrate a simple periodically locked cw cavity ringdown spectroscopy technique that enables a very large number of ringdown events to be rapidly acquired. An external cavity diode laser is locked to a high-finesse cavity, and as many as 16,000 ringdown events per second are obtained by periodically switching off the light entering the high-finesse cavity. Following each ringdown event, the light to the cavity is switched back on and cavity lock is rapidly reacquired. Limited only by our relatively modest digitization rate, we obtained a minimum detectable absorption loss of 4.7 x 10(-9) cm(-1), but we show that faster digitization could provide a sensitivity of 5.9 x 10(-10) cm(-1) Hz(-1/2).

Narrow-linewidth master-oscillator power amplifier based on a semiconductor tapered amplifier

The output of a grating-stabilized external-cavity diode laser was injected into a semiconductor tapered amplifier in a master-oscillator power amplifier configuration, producing as much as 500 mW of power with narrow linewidth. The additional linewidth that is due to the tapered amplifier is much smaller than the typical linewidth of grating-stabilized laser diodes. To demonstrate the usefulness of the narrow linewidth and high output power, we used the system to perform Doppler-free two-photon spectroscopy with rubidium.

Double-well magnetic trap for Bose-Einstein condensates

Clarendon Laboratory, Department of Physics, University of Oxford,Parks Road, Oxford, OX1 3PU, United Kingdom.(Dated: August 10, 2001)We present a magnetic trapping scheme for neutral atoms based on a hybrid of Ioffe-Pritchard andTime-averaged Orbiting Potential traps. The resulting double-well magnetic potential has readilycontrollable barrier height and well separation. This offers a new tool for studying the behavior ofBose condensates in double-well potentials, including atom interferometry and Josephson tunneling.We formulate a description for the potential of this magnetic trap and discuss practical issues suchas loading with atoms, evaporative cooling and manipulating the potential.

Suppression of collisional loss from a magnetic trap

Caesium atoms in a magnetic trap have a higher loss rate from intra-trap collisions than rubidium under comparable conditions. We have found that this loss from inelastic collisions can be suppressed by periodic optical pumping of the atoms back into the most strongly trapped magnetic state , although this reclamation of the strayed atoms gives rise to some heating of the sample. This observation shows that the dominant loss mechanism in the magnetic bias field regime investigated is from collisions which change the magnetic sublevel (quantum number ) and not the hyperfine level (F quantum number).

Nonlinear atom-optical {delta}-kicked harmonic oscillator using a Bose-Einstein condensate

We experimentally investigate the atom-optical {delta}-kicked harmonic oscillator for the case of nonlinearity due to collisional interactions present in a Bose-Einstein condensate. A Bose condensate of rubidium atoms tightly confined in a static harmonic magnetic trap is exposed to a one-dimensional optical standing-wave potential that is pulsed on periodically. We focus on the quantum antiresonance case for which the classical periodic behavior is simple and well understood. We show that after a small number of kicks the dynamics are dominated by dephasing of matter wave interference due to the finite width of the condensates initial momentum distribution. In addition, we demonstrate that the nonlinear mean-field interaction in a typical harmonically confined Bose condensate is not sufficient to give rise to chaotic behavior.

A simple laser cooling and trapping apparatus for undergraduate laboratories

We present detailed instructions for the construction of a pyramidal-style laser cooling and trapping apparatus. This scheme requires only a single beam, rather than the three pairs of orthogonal beams of the standard magneto-optical trap, which greatly simplifies the geometry and substantially reduces the cost. The trap is based largely on low-cost commercially available items and is simple to construct. It is remarkably insensitive to alignment and reliable to operate. Using a single laser beam with an intensity of 1.3 mW/cm2 we cool and trap more than 4 million rubidium atoms.

Output coupling of a Bose-Einstein condensate formed in a TOP trap

Two distinct mechanisms are investigated for transferring a pure 87Rb Bose-Einstein condensate in the |F = 2, mF = 2 state into a mixture of condensates in all the mF states within the F = 2 manifold. Some of these condensates remain trapped whilst others are output coupled in the form of an elementary pulsed atom laser. Here we present details of the condensate preparation and results of the two condensate output coupling schemes. The first scheme is a radio-frequency technique which allows controllable transfer into available mF states, and the second makes use of Majorana spin-flips to populate all the manifold sub-states equally.

Dynamical instabilities of Bose-Einstein condensates at the band edge in one-dimensional optical lattices

We present a joint theoretical and experimental study of the dynamical instability of a Bose—Einstein condensate at the band edge of a one-dimensional optical lattice. The instability manifests as rapid depletion of the condensate and conversion to a thermal cloud. We consider the collisional processes that can occur in such a system, and undertake a thorough theoretical study of the dynamical instability in systems of different dimensionality. We find spontaneous scattering is an important part of this process, and thus the Gross-Pitaevskii equation is unable to accurately predict the dynamics in this system. Our beyond mean-field approach, known as the truncated Wigner method, allows us to make quantitative predictions for the processes of parametric growth and heating that are observed in the laboratory, and we find good agreement with the experimental results.

Quantum scattering of distinguishable bosons using an ultracold-atom collider

We describe an implementation of a magnetic collider for investigating cold collisions between ultracold atomic clouds in different spin states, and we use this to study scattering involving both even- and odd-order partial waves. Our method relies on the axial asymmetry of a double-well magnetic trap to selectively prepare the spin state in each cloud. We measure the energy dependence of