Thermal intermodulation noise in cavity-based measurements
Abstract
Thermal frequency fluctuations in optical cavities limit the sensitivity of precision experiments ranging from gravitational wave observatories to optical atomic clocks. Conventional modeling of these noises assumes a linear response of the optical field to the fluctuations of cavity frequency. Fundamentally, however, this response is nonlinear. Here we show that nonlinearly transduced thermal fluctuations of cavity frequency can dominate the broadband noise in photodetection, even when the magnitude of fluctuations is much smaller than the cavity linewidth. We term this noise “thermal intermodulation noise” and show that for a resonant laser probe it manifests as intensity fluctuations. We report and characterize thermal intermodulation noise in an optomechanical cavity, where the frequency fluctuations are caused by mechanical Brownian motion, and find excellent agreement with our developed theoretical model. We demonstrate that the effect is particularly relevant to quantum optomechanics: using a phononic crystal membrane with a low-mass, soft-clamped mechanical mode, we are able to operate in the regime where measurement quantum backaction contributes as much force noise as the thermal environment does. However, in the presence of intermodulation noise, quantum signatures of measurement are not revealed in direct photodetection. The reported noise mechanism, while studied for an optomechanical system, can exist in any optical cavity.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Nov 10, 2020
- Source ID
- 10.1364/optica.402449
Entities
People
- Alberto Beccari
- Amirali Arabmoheghi
- Dalziel Joseph Wilson
- Nils J Engelsen
- Sergey Fedorov
- Tobias Kippenberg
Organizations
- Defense Advanced Research Projects Agency
- Horizon 2020
- Swiss National Science Foundation