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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.
Physical Review Letters
|April 25, 2026
Summary
We developed a new method to measure thermal noise in optical cavities, even below the quantum noise limit. This technique allowed us to achieve new benchmarks in sub-standard quantum limit optomechanical measurements.
Area of Science:
- Optomechanics
- Quantum Optics
- Materials Science
Background:
- Optical cavities are crucial for precision measurements.
- Thermal noise and quantum noise are fundamental limits in sensitive measurements.
- Previous work achieved sub-standard quantum limit (SQL) displacement sensitivity using an optical spring.
Purpose of the Study:
- To present a novel method for characterizing thermal noise in optical cavities, independent of quantum noise.
- To measure thermal noise below the quantum noise limit.
- To investigate quantum noise suppression using an optical spring effect.
Main Methods:
- Utilized a GaAs/AlGaAs micromirror on a GaAs cantilever microresonator in a Fabry-Pérot cavity at cryogenic temperatures (∼25 K).
- Employed an optical spring within the cavity to influence measurement sensitivity.
- Measured thermal noise contributions and quantum noise suppression below the standard quantum limit (SQL).
Main Results:
- Measured thermal noise falling up to 5 dB below the SQL.
- Observed quantum noise suppression up to 10 dB below the SQL due to the optical spring effect.
- Established a new benchmark for sub-SQL optomechanical measurements.
Conclusions:
- The developed method successfully characterizes thermal noise independently of quantum noise, even below the quantum noise limit.
- The optical spring effect significantly suppresses quantum noise, enabling unprecedented sub-SQL performance.
- This work advances the field of high-precision optomechanics and quantum measurement.
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