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Quantum Squeezing of Motion in a Mechanical Resonator


Wollman, Emma Edwina (2015) Quantum Squeezing of Motion in a Mechanical Resonator. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9CR5R97.


Quantum mechanics places limits on the minimum energy of a harmonic oscillator via the ever-present "zero-point" fluctuations of the quantum ground state. Through squeezing, however, it is possible to decrease the noise of a single motional quadrature below the zero-point level as long as noise is added to the orthogonal quadrature. While squeezing below the quantum noise level was achieved decades ago with light, quantum squeezing of the motion of a mechanical resonator is a more difficult prospect due to the large thermal occupations of megahertz-frequency mechanical devices even at typical dilution refrigerator temperatures of ~ 10 mK.

Kronwald, Marquardt, and Clerk (2013) propose a method of squeezing a single quadrature of mechanical motion below the level of its zero-point fluctuations, even when the mechanics starts out with a large thermal occupation. The scheme operates under the framework of cavity optomechanics, where an optical or microwave cavity is coupled to the mechanics in order to control and read out the mechanical state. In the proposal, two pump tones are applied to the cavity, each detuned from the cavity resonance by the mechanical frequency. The pump tones establish and couple the mechanics to a squeezed reservoir, producing arbitrarily-large, steady-state squeezing of the mechanical motion. In this dissertation, I describe two experiments related to the implementation of this proposal in an electromechanical system. I also expand on the theory presented in Kronwald et. al. to include the effects of squeezing in the presence of classical microwave noise, and without assumptions of perfect alignment of the pump frequencies.

In the first experiment, we produce a squeezed thermal state using the method of Kronwald et. al.. We perform back-action evading measurements of the mechanical squeezed state in order to probe the noise in both quadratures of the mechanics. Using this method, we detect single-quadrature fluctuations at the level of 1.09 +/- 0.06 times the quantum zero-point motion.

In the second experiment, we measure the spectral noise of the microwave cavity in the presence of the squeezing tones and fit a full model to the spectrum in order to deduce a quadrature variance of 0.80 +/- 0.03 times the zero-point level. These measurements provide the first evidence of quantum squeezing of motion in a mechanical resonator.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:squeezing, electromechanics, optomechanics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Schwab, Keith C.
Group:Institute for Quantum Information and Matter
Thesis Committee:
  • Schwab, Keith C. (chair)
  • Adhikari, Rana
  • Chen, Yanbei
  • Vahala, Kerry J.
Defense Date:28 May 2015
Record Number:CaltechTHESIS:05292015-131603299
Persistent URL:
Wollman, Emma Edwina0000-0002-5474-3745
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8924
Deposited By: Emma Wollman
Deposited On:02 Nov 2015 18:48
Last Modified:02 Jun 2020 21:51

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