Quantum weak torque sensing with squeezed optomechanics

Quantum-enhanced cavity optomechanical (COM) sensors, utilizing quantum resources, have become powerful tools for precisely measuring a wide range of physical quantities, from gravitational waves to accelerations. However, quantum-enhanced COM torque sensing remains an area of exploration. In this work, we show that utilizing quantum squeezing can suppress the quantum noise of a COM torque sensor below the standard quantum limit. We theoretically predict that our COM torque sensor can achieve an approximately 20-dB quantum advantage by optimizing the homodyne detection. Our approach is compatible with available engineering techniques of advanced COM sensors, with potential applications ranging from nanoscale magnetism to the quantum geometric phase.