Novel techniques for the trapping and manipulation of ultracold atoms

Abstract

We describe several novel techniques for the optical trapping of ultracold atoms and for the production of wavelength-stabilised, coherent light at the frequencies required for use in atomic physics experiments.

The greater part of this thesis deals with work towards the creation of regular arrays of microscopic optical dipole traps formed at the foci of truncated spherical cavities in a metallic film, in which the inter-site spacing can be set anywhere between one and several hundred micrometers. Arrays of such cavities are synthesised and structurally characterised via optical and electron microscopy, and numerical simulations of the light intensity distribution near the foci of such cavities under normal illumination are used to confirm their suitability for dipole trap production. A method for the construction of arrays of magneto-optical traps based on such structures is proposed and theoretically examined, and some preliminary experimental work towards the synthesis of the required microstructures is also described. Possible approaches to the loading of such traps and the imaging of the atoms contained therein are discussed - experimental work towards ballistic atom transfer from a specialised form of magneto-optical trap that can be formed close to a microstructured surface is carried out, and the efficacy of wavelength-selective fluorescence imaging as a means of reducing the effects of background scatter from the surface is experimentally demonstrated.

Further work described herein includes the proposal and experimental demonstration of two novel techniques for the removal of the carrier wave from a phase-modulated laser beam, one of which is based on a fiber-optic Mach-Zehnder interferometer that is shown to be an effective device for splitting or combining beams of nearly equal frequencies. A spontaneous-force based atom trapping mechanism that does not rely on the use of a magnetic field, but rather on spatially-dependent optical pumping between different metastable atomic states, is also proposed, and a proof of principle experiment is carried out to demonstrate the validity of the suggested mechanism. We find that this trapping scheme allows the spatial dependence of the trapping force to be tailored with a greater degree of flexibility than is usually possible with magneto-optical trapping, and that it is also capable of producing traps with stronger spring constants than are typically achievable with magneto-optical trapping under realistic experimental constraints.

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ORCID for T. Freegarde: orcid.org/0000-0002-0680-1330

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