Optomechanics with Superfluid Helium-4

Citation

De Lorenzo, Laura Anne (2016) Optomechanics with Superfluid Helium-4. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9RJ4GD7. https://resolver.caltech.edu/CaltechTHESIS:05272016-075803376

Abstract

We demonstrate the utility of superfluid helium-4 as an extremely low loss optomechanical element. We form an optomechanical system with a cylindrical niobium superconducting TE₀₁₁ resonator whose 40 cm³ inner cylindrical cavity is filled with ⁴He. [1] Coupling is realized via the variations in permittivity resulting from the density profile of the acoustic modes. Acoustic losses in helium-4 below 500 mK are governed by the intrinsic nonlinearity of sound, leading to an attenuation which drops as T ⁴, indicating the possibility of quality factors (Q) over 10¹⁰ at 10 mK. In our lowest loss mode, we demonstrate this T ⁴ law down to 50 mK, realizing an acoustic Q of 1.35·10⁸ at 8.1 kHz. When coupled with a low phase noise microwave source, we expect this system to be utilized as a probe of macroscopic quantized motion, for precision measurements to search for fundamental physical length scales, and as a continuous gravitational wave detector. Our estimates suggest that a resonant superfluid acoustic system could exceed the sensitivity of current broad-band detectors for narrow-band sources such as pulsars [2].

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