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Vers l’optomécanique quantique en arséniure de gallium : dissipation nanomécanique et opération pulsée

Abstract : During this doctoral work, we have designed, fabricated and characterised gallium arsenide (GaAs) optomechanical disk nano-resonators, in a cryogenic environment. These disks which bear highly coupled (g 0 ≈ MHz) GHz mechanical modes and telecom wavelength (λ ≈ 1550 nm) optical modes, show high mechanical (> 10^4 ) and optical (> 10^5 ) quality factors at 3 K. However, despite these state of the art performances, the optomechanical sideband cooling mechanism of the mechanical motion is not efficient enough to reach the quantum groundstate (less than 1 phonon in average). To determine the limiting factors, we have presented a systematical study of the mechanical dissipation channels and shown that two-level systems (TLS) at the surface of the material play a major role. We have also studied pulsed optical excitation of our resonators, in order to avoid absorption and thermal phenomena which limit the optomechanical cooling. We thus have underlined two main properties of the pulsed excitation : average injected optical power, and repetition period of the pulses with respect to the relaxation times of our systems. Alternative optical control schemes of the mechanical nanoresonators have emerged, which could be coupled to ultra-cold operation (T << 1 K).
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Mehdi Hamoumi. Vers l’optomécanique quantique en arséniure de gallium : dissipation nanomécanique et opération pulsée. Physique [physics]. Université Sorbonne Paris Cité, 2018. Français. ⟨NNT : 2018USPCC310⟩. ⟨tel-02935335v2⟩

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