Researchers have developed a sensor that uses a torsion pendulum and optical microcavity to measure the gravitational pull of millimeter-sized objects.

Researchers at Shanghai Jiao Tong University and other institutions have developed a new sensor capable of detecting the gravitational pull of millimeter-sized objects. Published in Nature Nanotechnology, the device utilizes a suspended torsion pendulum structure paired with an optical microcavity to measure minute gravitational forces. This development offers a new approach to sensing gravity at a microscopic scale, potentially aiding future research into the relationship between gravity and quantum physics.

Sensor Design and Mechanism

The sensor functions by using a torsion pendulum, a structure that twists its support when influenced by the gravitational pull of a nearby object. This movement is measured through an optical microcavity, which confines light and links it with vibrational energy. The interaction between light and vibrations creates a phenomenon the researchers call 'stopped light behavior,' which significantly slows the propagation of light pulses. This slowed light creates steep optical dispersion, allowing the sensor to convert nanoscale displacements into measurable optical signals.

Performance and Sensitivity

To test the sensor, the team periodically modulated the position of a millimeter-sized object and measured the resulting changes in gravitational force. The researchers reported a displacement sensitivity of 7.85 pm/√Hz and an acceleration sensitivity of 3.06 × 10 −16 g. By utilizing an evanescent field with a coupling length of approximately 100 nm, the device can resolve a minimum detectable gravitational-force change of 3.02 × 10 −16 N. The authors noted that this compact design improves upon traditional Cavendish-type torsion balances by integrating them with micro- and nanophotonic readout.