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High frequency GaAs whispering gallery resonators for quantum optomechanics

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In an « optomechanical system », light trapped in a cavity interacts with a mechanical oscillator. When this interaction is strong enough, photons can act on the oscillator dynamics, for example by « cooling » its motion. Many experiments in optomechanics aim at cooling down the oscillator to its motional ground state, to reveal its quantum behavior. This quantum regime is more easily accessible when the oscillator’s frequency is high.

In a recent work, we have explored the great potential of semiconductor optomechanical systems (1), by developing Gallium-Arsenide-based mechanical oscillators in form of miniature disks, whose vibration frequencies reach the GHz range (2). In these disks, light is trapped in a « whispering gallery mode », where it couples to the disk breathing mechanical motion. Thanks to the small mode volume of optical/mechanical interaction, the optomechanical coupling is extreme, several orders of magnitude above most current settings (the so-called vacuum coupling reaches 1 MHz). The mechanical Brownian motion of the disk is optically resolved with a sensitivity of 10^(-17)m/√Hz at room temperature, a record value for such a tiny and high frequency nanomechanical oscillator.

(1) L. Ding, C. Baker, P. Senellart, A. Lemaitre, S. Ducci, G. Leo, and I. Favero. ’High frequency GaAs nano-optomechanical disk resonator’. Physical Review Letters 105, 263903 (2010).

(2) L. Ding, C. Baker, P. Senellart, A. Lemaitre, S. Ducci, G. Leo, and I. Favero. ’Wavelength-sized GaAs optomechanical resonators with gigahertz frequency’. Applied Physics Letters 98, 113108 (2011).

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Very high frequency GaAs optomechanical resonators

In the figure below, different mechanical modes of GaAs disks are observed as a function of the disk radius