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Thesis Title: Ultra-low temperatures microwave optomechanics for quantum sensing

Recent advances in observing and exploiting macroscopic mechanical motion at the quantum limit brought opto-mechanical experiments down to always lower temperatures and smaller sizes, boosting a new research area were (more compatible) low energy photons are employed: microwave opto-mechanics. Superconducting microwave circuits are in use and bridge optomechanics with quantum electronics, which positions the former as a new resource for quantum information processing. But microwave opto-mechanical platforms provide also unique capabilities for testing quantum mechanics at the most basic level: if one thinks about these devices in terms of quantum-limited detectors, the focus is on the thermodynamic baths that continuously interact with the mechanical degree of freedom. The fundamental questions that are addressed are then quantum thermodynamics, the boundary between classical and quantum mechanics defined by wavefunction collapse, and ultra-low temperature materials properties.
In order to perform such experiments at the frontier of modern physics, we created a unique micro-wave/micro-Kelvin opto-mechanical platform. We demonstrate for the first time the passive cooling of a 15MHz aluminium drumhead mechanical device down to 500 micro-K, reaching a population for the fundamental mode of 0.3 quanta on average; all higher modes being empty to a very high probability. Using microwave opto-mechanics as a non-invasive detector, we report on the in-equilibrium thermal properties of this lowest frequency mode, challenging theory in an unprecedented experimental area.

Dylan Cattiaux died tragically in the mountains after his defense at the age of 26. He had already been awarded for his thesis by the MecaQ research group, which wished to name the "Optomechanics and Nanomechanics Thesis Prize" after the first prize-winning doctor. From now on, it will be called the "Dylan Cattiaux Prize". To know more

Key Words: Ultra-low temperatures, Optomechanics, Quantum limit, Nonlinearity, Nanomechanics

Doctoral School: ED de Physique
Research Laboratory: Institut Néel (CNRS)
Thesis Supervision:  Eddy COLLIN and Xin ZHOU

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