Integrated Quantum Optical Phase Sensor

TL;DR

This paper demonstrates a photonic integrated circuit in lithium niobate that generates squeezed light for quantum-enhanced phase sensing, advancing the development of deployable quantum sensors beyond laboratory settings.

Contribution

The authors present a lithium niobate integrated photonic circuit capable of producing squeezed states and enhancing phase measurement sensitivity, enabling practical quantum sensors.

Findings

Achieved 2.7% squeezing with 26.2 mW power

Integrated on-chip system enhances phase measurement sensitivity

Operates with low power and integrated functionality

Abstract

The quantum noise of light fundamentally limits optical phase sensors. A semiclassical picture attributes this noise to the random arrival time of photons from a coherent light source such as a laser. An engineered source of squeezed states suppresses this noise and allows sensitivity beyond the standard quantum limit (SQL) for phase detection. Advanced gravitational wave detectors like LIGO have already incorporated such sources, and nascent efforts in realizing quantum biological measurements have provided glimpses into new capabilities emerging in quantum measurement. We need ways to engineer and use quantum light within deployable quantum sensors that operate outside the confines of a lab environment. Here we present a photonic integrated circuit fabricated in thin-film lithium niobate that provides a path to meet these requirements. We use the second-order nonlinearity to produce a squeezed state at the same frequency as the pump light and realize circuit control and sensing with electro-optics. Using a 26.2 milliwatts of optical power, we measure (2.7 $\pm$ 0.2 )$\%$ squeezing and apply it to increase the signal-to-noise ratio of phase measurement. We anticipate that on-chip photonic systems like this, which operate with low power and integrate all of the needed functionality on a single die, will open new opportunities for quantum optical sensing.