Entangled Radiofrequency-Photonic Sensor Network*

Quantum metrology enables a measurement sensitivity below the standard quantum limit (SQL), as demonstrated in the Laser Interferometer Gravitational-wave Observatory (LIGO). As a unique quantum resource, entanglement has been utilized to enhance the performance of, e.g., microscopy, target detection, and phase estimation. To date, almost all existing entanglement-enhanced sensing demonstrations are restricted to improving the performance of probing optical parameters at a single sensor, but a multitude of applications rely on an array of sensors that work collectively to undertake sensing tasks in the radiofrequency (RF) and microwave spectral ranges. Here, we propose and experimentally demonstrate a reconfigurable RF-photonic sensor network comprised of three entangled sensor nodes. We show that the entanglement shared by the sensors can be tailored to substantially increase the precision of parameter estimation in networked sensing tasks, such as estimating the angle of arrival (AoA) of an RF field. The entangled RF-photonic sensor network achieves an estimation variance 3.2 dB below the SQL in measuring the average field amplitudes and an estimation variance 3.5 dB (3.2 dB) below the SQL in measuring the AoA at a central (edge) node. Our work would open a new avenue toward utilizing quantum metrology for ultrasensitive positioning, navigation, and timing.