Brillouin optomechanics in whispering-gallery-mode microresonators: From strong coupling to single-phonon-level control

Cavity quantum optomechanics aims to utilize the tools of quantum optics to generate and study quantum states of motion of mechanical resonators and has recently undergone a surge of growth owing to its potential to contribute to both fundamental and applied physics. Within the field, several different experimental systems are pursued across the globe, including Fabry-Perot cavities with movable mirrors, levitated optomechanical systems, and other nano-optical implementations, each having their own advantages and disadvantages. In this talk, a new experimental direction--Brillouin optomechanics--will be discussed, which unites several favourable properties including very high mechanical frequencies (~ 10 GHz), very low optical loss and absorption, and back-scatter operation which makes it a favourable candidate to overcome existing experimental roadblocks to engineer and utilize quantum states at a macroscopic scale. This talk will focus on two of our team's most recent results in this direction: (i) the observation of Brillouin optomechanical strong coupling between the optical cavity field and these high-frequency mechanical vibrations, which enables optical control at a rate that exceeds the system's decay rates [1], and (ii) performing heralded single-phonon addition and subtraction to a mechanical thermal state, which has the counterintuitive effect of approximately doubling the mean thermal occupation [2]. This research opens a rich avenue for further studies that test the very foundations of quantum mechanics and for the development of powerful new quantum technologies, such as quantum memories and transducers.
[1] Enzian et al. Optica 6, 7 (2019).
[2] Enzian et al. arXiv:2006.11599 (accepted in Phys. Rev. Lett.).
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