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Cryogenic Optomechanics with Silica Microresonators Open Access


Other title
low temperature imaging
dilution refrigeration
optical resonators
tapered fiber
mechanical mode thermometry
Type of item
Degree grantor
University of Alberta
Author or creator
MacDonald, Allison J. R.
Supervisor and department
Davis, John (Physics)
Examining committee member and department
LeBlanc, Lindsay (Physics)
Freeman, Mark (Physics)
Davis, John (Physics)
Hegmann, Frank (Physics)
Department of Physics

Date accepted
Graduation date
Master of Science
Degree level
Cavity optomechanical devices are interesting systems for probing quantum mechanical behaviour of mesoscopic objects. A basic requirement for these types of experiments is preparation of the mechanical resonator in, or at least very close to, its ground state. Although active laser cooling techniques can help this process, conventional cryogenic (pre-)cooling is nonetheless necessary. This thesis introduces a custom-made apparatus, housed on the base plate of a commercial dilution refrigerator, for coupling light into an optomechanical resonator via a tapered optical fiber. Our system incorporates full three-dimensional control of the taper-resonator coupling conditions, enabling critical coupling at cryogenic temperatures. It also features an optical microscope which permits in situ imaging and alignment of the taper and resonator, while causing minimal heating to the environment. Optomechanical measurements of silica bottle resonators, which exhibit optical whispering gallery modes and high-quality mechanical breathing modes, are performed using the dilution fridge system. Several methods for enhancing the detection of small mechanical signals are tested and a method for determining the temperature of the mechanical mode is described and implemented. The tight confinement of light circulating in the bottle resonator leads to increased optical absorption and significant heating of the silica, which manifests itself in both the optical and mechanical properties of the resonator. We present the first measurements of these resonators for mechanical mode temperatures as low as 4 K, and fridge temperatures down to 9 mK.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
A. J. R. MacDonald, G. G. Popowich, B. D. Hauer, P. H. Kim, A. Fredrick, X. Rojas, P. Doolin and J. P. Davis, "Optical microscope and tapered fiber coupling apparatus for a dilution refrigerator", Rev. Sci. Inst. 86, 013107 (2015)

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