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Updated: Apr 27, 2026

Fabrication and Testing of Photonic Thermometers
Published on: October 24, 2018
Thermal Noise Measurement below the Standard Quantum Limit
Ronald Pagano1, Scott Aronson1, Torrey Cullen2
1Louisiana State University, Department of Physics and Astronomy, Baton Rouge, Louisiana, 70803, USA.
None:
We present a method characterizing thermal noise in an optical cavity independent from quantum noise despite the thermal noise falling below the quantum noise limit. Using this method, we measured the thermal noise contribution from a GaAs/AlGaAs micromirror suspended on a GaAs cantilever microresonator when brought to a cryogenic temperature (∼25 K) and incorporated into a Fabry-Pérot cavity. An optical spring is formed in this optical cavity. Previously, this setup exploited an optical spring to produce a displacement sensitivity falling 2.8 dB below the free-mass standard quantum limit (SQL), as reported by Cullen et al. [Phys. Rev. Lett. 133, 113602 (2024)PRLTAO0031-900710.1103/PhysRevLett.133.113602]. Here we use a similar setup to measure thermal noise which fell a maximum of 5 dB below the SQL. This measurement, in turn, allowed for an investigation of quantum noise suppression resulting from the optical spring effect, falling a maximum of 10 dB below the SQL, a new benchmark for sub-SQL optomechanical measurements.
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