Magnetic Field Tomography

Neutral atoms may be trapped via the interaction of their magnetic dipole moment with magnetic field gradients. One of the possible schemes is the cloverleaf trap. It is often desirable to have at hand a fast and precise technique for measuring the magnetic field distribution. We introduce a novel diagnostic tool for instantaneous imaging the equipotential lines of a magnetic field within a region of space (the vacuum recipient) that is not accessible to massive probes. Our technique is based on spatially resolved observation of the fluorescence emitted by a hot beam of sodium atoms crossing a thin slice of resonant laser light within the magnetic field region to be investigated. The inhomogeneous magnetic field spatially modulates the resonance condition between the Zeeman-shifted hyperfine sublevels and the laser light and therefore the amount of scattered photons. We demonstrate this technique by mapping the field of our cloverleaf trap in three dimensions under various conditions.Comment: 8 pages, 8 figure

Using Photo-Associative Ionization of Sodium to Demonstrate t he Opt ical Control of Cold Collisions

LVe present a study of cold collisions in a sample of magneto-optically trapped sodium atoms througli the technique of two-color photoassociative ionization spectroscopy. We demonstrate the inhibition of the process by adding an auxiliary %uppressor" laser beam and analyze tlie dependence of this optical shielding effect on the laser frequency and intensity. The possibility of using photons to control the atomic collision and to modify the thermodynamic properties of tlie cold gas is discussed. Tlie study of collisions involving laser cooled and trapped atorns has been the subject of intense investigations during the past few years. TIiis interest has been motivated by tlie desire of achieving the regime of a degenerated quantum gas and also by intrinsic features it presents, inainly tliat in tlie presence of light, collisions involving excited state atoms have duration comparable to the spontaneous emission time. In this regime, the exchange of energy between the atom ,and the modes of the radiation field (including vacuum) provides a prototype for studying the properties of nonequilibrium open systems coupled to reservoirs. As the kinetic energy of a two-body collision approaches zero, the number of partia1 waves coiitributing to the elastic collision reduces to one, the s-wave, and the information about the atomic interaction is comyletely contained in the scattering length a. The properties of a cold gas are therefore dependent on the scattering lengtli and its sign can determine the behavior of the system. Tlie recente achievement of the quantum gas regime iii a sample of laser cooled and magnetic trapped rubidium atoms[lI has opened new possibilities of studies involving the thermodymanics of a gas in such regime. Controlling the atomic interaction with photons can provide the condition to stabilize tlie gas in a single quantum state of the confining potential and also the manipulation of its thermodynamical properties. We liave recently demonstrated the possibility of controlling the atomic interaction by using photo-associative ionization (PAI) in a sample of cold sodium atoms held in a trapt2]. In this paper we present the studies of cold collisions using PAI as a prototype and the route we liave taken towards the demonstration of optical control of cold collisions. We discuss the possibility of using photons as a to01 to cliange the course of the atomic encounter, including the modification of attraction into repulsion aiid its applications. Photo-associative ionization as a prototype of cold collisions Conventional associative ionization occurring at ordinary temperatures proceeds in two distinct steps: excitation of isolated atoms followed by the collisional interaction between excited atomic states. Tlie collision event is fast compared to the radiative relaxation and the two steps are decoupled. In contrast, PAI starts with ground state partners moving sufficiently slow that they have time to absorb and spontaneously emit photons prior to the final ionizing interaction. The partners inust be close enough when the initial absorption takes place such tliat a significant fraction of the excited population survives to relaxation back to the ground state. Thus, PAI starts by promoting the ground state of the colliding species, designated by [Na,,Na], to a

Radiative lifetime measurements of rubidium Rydberg states

We have measured the radiative lifetimes of ns, np and nd Rydberg states of rubidium in the range 28 < n < 45. To enable long-lived states to be measured, our experiment uses slow-moving Rb atoms in a magneto-optical trap (MOT). Two experimental techniques have been adopted to reduce random and systematic errors. First, a narrow-bandwidth pulsed laser is used to excite the target Rydberg state, resulting in minimal shot-to-shot variation in the initial state population. Second, we monitor the target state population as a function of time delay from the laser pulse using a short-duration, millimetre-wave pulse that is resonant with a one- or two-photon transition. We then selectively field ionize the monitor state, and detect the resulting electrons with a micro-channel plate. This signal is an accurate mirror of the target state population, and is uncontaminated by contributions from other states which are populated by black body radiation. Our results are generally consistent with other recent experimental results obtained using a less sensitive method, and are also in excellent agreement with theory.Comment: 27 pages,6 figure

Raman Spectroscopy of Mott insulator states in optical lattices

We propose and analyse a Raman spectroscopy technique for probing the properties of quantum degenerate bosons in the ground band of an optical lattice. Our formalism describes excitations to higher vibrational bands and is valid for deep lattices where a tight-binding approach can be applied to the describe the initial state of the system. In sufficiently deep lattices, localized states in higher vibrational bands play an important role in the system response, and shifts in resonant frequency of excitation are sensitive to the number of particles per site. We present numerical results of this formalism applied to the case of a uniform lattice deep in the Mott insulator regime.Comment: 10 pages, 3 figure