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Foxon, Bethany (2021) Quantum coherence control for radio-frequency dressed cold atom systems. PhD thesis, University of Nottingham.

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Abstract

The ability to understand and control the internal state of the atom is essential to cold atom schemes. From quantum memories and fundamental physics experiments to timekeeping and inertial sensing, precise state manipulation is a key element. The use of static and AC-dressing fields can generate complex potential geometries, such as optical lattices, shell traps and toroidal shapes. However, the increased complexity of these topologies presents a number of complications which need to be addressed.

The first question is one of control. The use of radio-frequency dressing to couple between magnetic sublevels in the ground state of an alkali atom can enable multi-photon transitions between arbitrary pairs of energy levels. In this thesis, we study the structure of rubidium 87 with such a dressing, with its many emergent quasi-energy levels. Of particular interest are the couplings between hyperfine levels, which are studied both theoretically and experimentally. We measure the relative population in each of the hyperfine levels utilising the linear birefringence properties of the atom. A commonpath, homodyne interferometer is used to convert polarisation change into a measure of population. We can thus determine the internal state of the atom, as well as measuring transition frequencies and coupling strengths, including their dependence on static magnetic field. Pure magnetic substates can be produced and studied using a series of optical and microwave pulses. State labelling can also be performed, as the sign of the polarisation shift differs between states. The introduction of a common mode suppressed state detection scheme provides an improved method of measurement.

Building on this knowledge of the dressed level system, this thesis also presents work towards the generation of robust, trappable pairs of clock states for use in quantum technology. We begin with a pair of trappable states whose potentials have a similar response to static magnetic field. The frequency of the transition between these two states will still exhibit field dependence however, due to differences in the magnitude of the Lande g-factors between hyperfine manifolds. In order to coherently control these states, for use in state dependent guiding or quantum memories, this mismatch in the potentials needs to be cancelled. By use of the AC-Zeeman effect to tune the relevant level energies, increased robustness is demonstrated. The reduction in field dependence can be achieved to higher orders using a number of dressings at different frequencies and powers, with data using dressings to second order presented here. We demonstrate a reduction in field dependence to less than the resolution-limited linewidth over our trappable range.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Fernholz, Thomas Lesanovsky, Igor
Keywords:	Quantum coherence control, Radio-frequency dressed cold atom systems
Subjects:	Q Science > QC Physics > QC170 Atomic physics. Constitution and properties of matter
Faculties/Schools:	UK Campuses > Faculty of Science > School of Physics and Astronomy
Item ID:	64684
Depositing User:	Foxon, Bethany
Date Deposited:	31 Jul 2021 04:40
Last Modified:	31 Jul 2021 04:40
URI:	https://eprints.nottingham.ac.uk/id/eprint/64684

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