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A laser based accelerator for ultracold atoms

Published Jan 1, 2012• 0 citations
OpenAlex

Abstract

We present first results on our implementation of a laser based accelerator for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and accelerated by means of laser tweezer beams and the atomic scattering is directly observed in laser absorption imaging. The optical collider has been characterized using 87Rb atoms in the |F = 2,mF = 2 〉 state, but the scheme is not restricted to atoms in any particular mag-netic substates and can readily be extended to other atomic species as well. c © 2012 Optical Society of America OCIS codes: 350.4855, 020.2070, 020.7010, 020.1475. The scattering experiment has been described as the most important experimental technique in quantum physics [1]. Typical textbook treatments describe the problem in terms of a beam impinging on a target: par-ticles collide along a well-defined axis with respect to which the angular scattering distribution of particles is determined. Knowledge about collision properties of neu-tral atoms at extremely low energies has been of crucial importance for developing the field of ultracold atomic

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We present first results on our implementation of a laser based accelerator for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and accelerated by means of laser tweezer beams and the atomic scattering is directly observed in laser absorption imaging. The optical collider has been characterized using 87Rb atoms in the |F = 2,mF = 2 〉 state, but the scheme is not restricted to atoms in any particular mag-netic substates and can readily be extended to other atomic species as well. c © 2012 Optical Society of America OCIS codes: 350.4855, 020.2070, 020.7010, 020.1475. The scattering experiment has been described as the most important experimental technique in quantum physics [1]. Typical textbook treatments describe the problem in terms of a beam impinging on a target: par-ticles collide along a well-defined axis with respect to which the angular scattering distribution of particles is determined. Knowledge about collision properties of neu-tral atoms at extremely low energies has been of crucial importance for developing the field of ultracold atomic
We present our first results on our implementation of a laser based accelerator for ultracold atoms. Atoms cooled to a temperature of 420 nK are confined and accelerated by means of laser tweezer beams, and the atomic scattering is directly observed in laser absorption imaging. The optical collider has been characterized using 87Rb atoms in the |F=2, m(F)=2] state, but the scheme is not restricted to atoms in any particular magnetic substates and can readily be extended to other atomic species as well.
This thesis describes the construction of a dual species setup using fermionic 40K and bosonic 87Rb with the goal of cooling to ultracold temperatures and quantum degeneracy, and also perfoming precision collision experiments using a novel optical collider. The setup is composed of a dual species magneto-optical trap, with transfer to an ultrahigh vacuum science cell achieved using a mechanical transport scheme. Atoms are cooled to ultracold temperatures using forced radio frequency evaporation in a Ioffe-Pritchard style magnetic trap. The optical collider utilises the optical dipole force to trap a sample of ultracold atoms and accelerate them towards a target sample using an acousto-optic modulator. The process of cooling 87Rb atoms in the |F = 2, mF = 2> hyperfine state to Bose-Einstein condensation is described, as well as progress towards production of ultracold 40K. Design, implementation, and characterisation of the optical collider is provided, showing that it is a precision metrology device.
This thesis describes experiments investigating the collisions of alkali metal atoms at energies between 10 - 2000 uK, measured in units of the Boltzmann constant. The atoms are accelerated towards each other using a purpose-built collider comprised of a crossed-beam optical dipole trap, which enables us to collide dense ensembles of ultracold atoms in any internal state at relatively high energies. I present the results of two experiments centered around resonant enhancement of the collisions. The first is between homonuclear 40K atoms near a shape resonance where the fermionic nature of the atoms determines the character of multiple scattering effects. The second experiment involves heteronuclear 40K87Rb collisions near a magnetically-tunable Feshbach resonance where we measure parameters describing the resonance as a function of collision energy. Theoretical models are developed that let us describe the collisions using published empirical interaction potentials, and we find good agreement between these models and the experiment.
We report on experiments investigating the collisional properties of atoms at ultralow collision energies using an all-optical atom collider. By using a pair of optical tweezers, we can manipulate two ultracold atom clouds and collide them together at energies up to three orders of magnitude larger than their thermal energy. Our experiments measure the scattering of 87 Rb, 40 K, and 40 K- 87 Rb collisions. The versatility of our collider allows us to probe both shape resonances and Feshbach resonances in any partial wave. As examples, we present experiments demonstrating p-wave scattering with indistinguishable fermions, inelastic scattering at non-zero energies near a homonuclear Feshbach resonance, and partial wave interference in heteronuclear collisions.
Advances in laser cooling of neutral atoms have made possible a new form of high resolution spectoscopy: photoassociation of ultracold atoms. Colliding neutral atoms, confined in a laser trap, are photoassociated to bound excited states of the dimer molecule by absorbing a photon from a tunable laser. The technique can probe long range and {open_quote}purely long range{close_quote} molecular states that are difficult or impossible to detect by traditional means and, because of the extremely low energy of the colliding atoms (1 mK), is capable of high resolution (0.001 cm{minus}1). Recent results include, the first direct (and most precise) measurement of a molecular dissociation limit, the first observation of retardation effects in atom-atom interactions, high precision measurements of atomic lifetimes, and the study of exotic states of alkali dimers.
During the last few decades, the two fields of ultracold neutral atoms and of single trapped ions have undergone an amazing development. The incorporation of these systems into a single experiment exploits the complementary physical properties of the subsystems and opens up novel lines of research. I present experimental results obtained in one of the first hybrid atom-ion setups accessing the cold regime. Single ions interact with ultracold samples of 87Rb atoms. The collision energies are set by heating mechanisms in the Paul trap and are on the order of mK·kB. Interactions are generally strong and long-ranged. We observe elastic atom-ion scattering in the semi-classical energy regime in which the cross section depends on the collision energy and favors scattering at small angles. We were able to obtain a general good understanding of atom-ion two-body collisions. We observed sympathetic cooling of the ion over four orders of magnitude in energy through collisions with the ultracold atoms. Further, we utilized atom-ion scattering events to develop a novel method to compensate excess ion micromotion, the primary source of ion heating. Three-body collisions between two atoms and the ion play an important role. We identified these processes through the large amounts of energy that they release. This makes them detectable despite their suppression with respect to two-body collisions. We also showed that atom-ion three-body collisions become more prominent as the collision energy decreases. Finally, we employed our atom-ion apparatus to gain novel insights into three-body recombination between ultracold atoms. In these experiments the ion trap acts as an extremely sensitive ion detector. Through three-body recombination a Rb2 molecule is formed and can undergo ionization by absorbing photons from a strong laser. By scanning the frequency of the ionization laser we obtained a molecular spectrum and identified a relatively broad distribution over final molecular states.