# High-fidelity detection of a phase shift using non-Gaussian quantum states of light

## TL;DR

This paper demonstrates that injecting non-Gaussian quantum states into an interferometer enables highly sensitive phase shift detection, significantly outperforming traditional Gaussian-state methods when using advanced photon detectors.

## Contribution

The study introduces a method using non-Gaussian quantum states and squeezing techniques to enhance phase shift detection fidelity beyond Gaussian limits.

## Key findings

- Detection error reduced by nearly an order of magnitude with non-Gaussian states.
- High-efficiency photon detectors improve measurement precision.
- Squeezing and anti-squeezing techniques further enhance sensitivity.

## Abstract

We show that by injecting a light pulse prepared in a non-Gaussian quantum state into the dark port of a two-arm interferometer, it is possible to detect a given phase shift with the fidelity which is limited only by the optical losses and the photodetection inefficiency. The value of the phase shift is inversely proportional to the amplitude of the classical carrier light injected into another (bright) port of the interferometer. It can be reduced by using an additional degenerate parametric amplifier (squeezer) in the input dark port and the matching anti-squeezer in the output dark port. We show that using the modern high-efficiency photon number resolving detectors, it is possible to reduce the detection error by almost one order of magnitude in comparison with the ordinary (Gaussian-state) interferometry.