Cryogenic Optomechanics with Silica Microresonators

• Author / Creator

  MacDonald, Allison J. R.

• 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.

• Subjects / Keywords

  • Dilution refrigeration
  • Optomechanics
  • Tapered fiber
  • Low temperature imaging
  • Optical resonators
  • Mechanical mode thermometry

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R36W96H85

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.