A Low-Noise Electrically Levitated Oscillator for Investigating Fundamental Physics

Abstract

This thesis describes the creation of a low-noise, electrodynamically levitated nanoparticle oscillator for applications in optomechanics and quantum physics. The harmonic motion of a nanoparticle trapped in a linear Paul trap was measured and characterized. Velocity damping and parametric feedback cooling methods were implemented to cool the centre-of-mass motion of an oscillator. Experiments were conducted on the same particle so that a direct comparison between both methods could be done. Theory and simulations were developed to fully understand these processes. It was shown that velocity damping achieves lower temperatures due to the greater backaction from measurement noise in the parametric feedback scheme. A minimum temperature of $26\pm6$\,mK was reached in these experiments limited only by detection noise. Low-noise electronics, designed to prevent motional heating of the levitated nanoparticle due to fluctuations in the confining electric fields, were studied. At low pressures down to 3×10⁻⁷ mbar, where minimal thermal noise is present from gas collisions, no heating effect from voltage fluctuations was observed in two of the oscillator modes. This work demonstrated the utility of this trap for future low-noise experiments including investigations into wave function collapse with preliminary results presented here. The cooling and dynamics of two co-trapped nanoparticles strongly coupled by their mutual Coulomb repulsion was also studied. The normal modes in both the axial and radial motion of the trapped nanoparticle were measured and characterized. Sympathetic cooling and squeezing of one particle were achieved through interaction with the other trapped nanoparticle. Temperatures down to 200±10 mK and 190±40 mK were reached in the axial normal modes. Additionally, a measurement-based scheme was used to couple the axial normal modes which were shown to display the characteristics of strong coupling. Energy exchange between the two modes was demonstrated alongside sympathetic cooling of one mode through this coupling