Quantum Optics Seminar by Nils Johan Engelsen

Ultralow dissipation mechanical resonators for sensing and optomechanics

Nanomechanical oscillators are among the most sensitive force and acceleration sensors and show promise as a quantum technology. However, their performance is fundamentally limited by mechanical dissipation, which admits thermomechanical noise from the environment, limiting force sensitivity, and cuts down the coherence time of mechanical quantum states. At the same time, reduced size allows stronger coupling to other degrees of freedom such as electromagnetic fields. These two demands are conflicting: due to surface losses, smaller size typically leads to increased dissipation. However, the phenomenon ‘dissipation dilution’, where mechanical losses are diluted by stress, breaks this trend. Over the last decade, dissipation dilution has been exploited to reduce the dissipation of nanomechanical resonators by three orders of magnitude; thereby allowing nanomechanical oscillators to surpass the quality factors of the best macroscopic oscillators. In this talk, I will show how dissipation dilution is greatly enhanced by engineering the resonator geometry and how we exploit this to demonstrate record mechanical quality factors at room temperature (3.6 billion) and cryogenic temperatures (13 billion).
Towards the end of my talk, I will show how we use ultrahigh-Q mechanical resonators in optomechanical systems to demonstrate quantum optomechanical effects at room temperature—a longstanding challenge of the field due to the large thermal fluctuations drowning out the minute effects of quantum fluctuations in radiation pressure.