Photonic quantum metrology with variational quantum optical non-linearities

TL;DR

This paper introduces a variational quantum optical protocol that efficiently generates high-quality, noise-robust photonic states for quantum metrology, overcoming scalability issues of previous methods.

Contribution

It combines quantum optical non-linearities with variational algorithms to produce metrologically useful states with fewer operations, enhancing fidelity and noise resilience.

Findings

Exponential improvement in state fidelity with gate errors.

Enhanced robustness of generated states against noise.

Scalable protocol compatible with current cavity QED setups.

Abstract

Photonic quantum metrology harnesses quantum states of light, such as NOON or Twin-Fock states, to measure unknown parameters beyond classical precision limits. Current protocols suffer from two severe limitations that preclude their scalability: the exponential decrease in fidelities (or probabilities) when generating states with large photon numbers due to gate errors, and the increased sensitivity of such states to noise. Here, we develop a deterministic protocol combining quantum optical non-linearities and variational quantum algorithms that provides a substantial improvement on both fronts. First, we show how the variational protocol can generate metrologically-relevant states with a small number of operations which does not significantly depend on photon-number, resulting in exponential improvements in fidelities when gate errors are considered. Second, we show that such states offer a better robustness to noise compared to other states in the literature. Since our protocol harnesses interactions already appearing in state-of-the-art setups, such as cavity QED, we expect that it will lead to more scalable photonic quantum metrology in the near future.