Approaching the standard quantum limit of mechanical torque sensing

Area of Science:

• Physics
• Quantum Mechanics
• Optomechanics

Background:

• Mechanically based torque sensors benefit from reduced moment of inertia for increased sensitivity.
• Measuring small displacements in such sensors presents a significant challenge.
• Cavity optomechanics offers enhanced readout by co-localizing optical and mechanical resonances.

Purpose of the Study:

• To develop a torque sensor with enhanced sensitivity by integrating cavity optomechanics.
• To overcome the limitations of thermal noise in optomechanical torque sensors.
• To investigate the performance of cryogenic optomechanical torque sensors at millikelvin temperatures.

Main Methods:

• Incorporation of cavity optomechanics to enhance sensor readout.
• Cooling a cavity-optomechanical torque sensor to ultra-low temperatures (25 mK).
• Measurement of torque sensitivity at cryogenic conditions.

Main Results:

• Demonstrated a torque sensitivity of 2.9 yNm/√Hz at 25 mK.
• The sensor's sensitivity is limited by quantum noise at cryogenic temperatures.
• Achieved sensitivity is a factor of ten above the quantum-limited sensitivity.

Conclusions:

• Cryogenic optomechanical torque sensors enable highly sensitive static and dynamic measurements.
• The developed sensor can measure integrated samples at the level of a few hundred spins.
• This technology advances the field of precision torque sensing at the quantum limit.