Optomechanics with an electrodynamically levitated oscillator

In this work I report on a hybrid trap platform for sensitive optomechanics experiments with applications in quantum physics, thermodynamics and material science. We characterise a miniature linear Paul trap which can be used in combination with an optical cavity. The low-frequency harmonic motion of a nanoparticle levitated in a Paul trap can be detected with competitive sensitivities using a super-resolution imaging technique. This same method can be applied to characterise trap stability and nanosphere parameters such as mass with a 3% uncertainty. Using this same method at room temperature and at pressure of 3×10⁻⁷ mbar, we were able to measure an ultra-narrow mechanical linewidth of ∼80 µHz with a novel phase sensitive scheme which removes slow drifts in the mechanical frequency. We used this measurement to place new bounds on dissipative versions of wavefunction collapse models. Using two optical cavity modes with different frequencies interacting with a nanoparticle levitated within a Paul trap realises a versatile optomechanical system, which can be operated in regimes dominated by either linear or quadratic optomechanical coupling. We demonstrated cooling of the centre-of-mass motion of the nano-oscillator exclusively provided by the quadratic coupling. This nonlinear interaction gives rise to a highly non-thermal state of motion which matches well with theoretical predictions. In the linear regime, we report cooling down to Teff=21±4 mK limited by Paul trap noise, demonstrating stable trapping in the cavity standing-wave down to pressures ∼10⁻⁶ mbar. Using the same technique, we show that in theory, near ground state cooling could be achieved with better electronics used in conjunction with the filtering cavity developed as part of this work