PhD Defense: Eric Planz

Electro- and opto-mechanics with soft-clamped membrane resonators at milliKelvin temperatures for quantum memory and transduction

The unique design of soft-clamped membrane mechanical resonators allows for low mechanical decay rates of 1 mHz at 1.5 MHz resonance frequency and to reach coherence times exceeding 140 ms, making them a promising component in emerging quantum technologies. This PhD defense presents advances and challenges in coupling electromagnetic fields in both the microwave and optical domains to such mechanical resonators at milliKelvin temperatures as a candidate for quantum memory and low-noise transduction.

 We attained high cooperativities in coupling microwave fields to membrane resonators. This allowed us to successfully cool an electro-mechanical system to its quantum ground state while identifying heating effects. We further implemented and initially tested solutions to further increase electro-mechanical systems while mitigating this heating effect.

 Harnessing strong optomechanical coupling in dry dilution refrigerators has been challenging due to vibration issues and heating by optical absorption. We addressed these issues with an actuator-free optical cavity and mechanical resonator design, in which the cavity is mounted on a simple vibration-isolation platform. We observed dynamical backaction when the cavity is driven with a free-space optical beam stabilized close to the red sideband using a two-beam locking scheme. Finally, we characterized the effect of absorption heating on the coherence time and found a scaling with the intracavity power P as tau proportional to P to the power of -(0.34+/-0.04).

 The findings from this work solve challenges in creating hybrid electro- and optomechanical systems within a singular setup, positioning electro-optomechanics as a prospective platform for achieving reduced noise transduction.