Quantum Fisher information in many-photon states from shift current shot noise

TL;DR

This paper proposes a method to directly measure the quantum Fisher information of nonclassical light using shift current shot noise, revealing quantum correlations hidden from conventional detection.

Contribution

It introduces a theoretical approach to access quantum Fisher information via shift current shot noise, enabling direct detection of quantum correlations in nonclassical light.

Findings

Shot noise Fano factor is proportional to photon number variance.

Integrated current depends only on mean photon number.

Numerical validation with Schrödinger cat and squeezed vacuum states.

Abstract

Quantum Fisher information (QFI) sets the ultimate precision of optical phase measurements and reveals multiphoton entanglement, but it is not accessible with conventional photodetection. We theoretically predict that a photodetector utilizing the shot noise of the quantum-geometric shift current of exciton polaritons can directly measure the QFI of nonclassical light. By solving the Lindblad equation, we obtain the time-dependent nonlinear photocurrent for an arbitrary initial photon state. It turns out that, regardless of the quantum state of the incident light, the integrated current depends only on the mean photon number. In stark contrast, the shot noise retains the quantum information: its Fano factor is proportional to the photon number variance and therefore encodes the QFI. Numerical calculations confirm these relations for illumination with optical Schr\"odinger cat and squeezed vacuum states. Quantum correlations in nonclassical light, usually hidden from direct detection, become observable in the form of shift current shot noise