Characterizing Biphoton Spatial Wave Function Dynamics with Quantum Wavefront Sensing

TL;DR

This paper introduces a novel quantum wavefront sensing method to efficiently characterize the spatial wave function of entangled photon pairs, capturing amplitude and phase information without the need for references or extensive tomography.

Contribution

The authors develop and demonstrate a reference-free quantum Shack-Hartmann wavefront sensing technique for biphoton spatial wave function measurement, advancing quantum optical field characterization.

Findings

Biphoton amplitude correlation weakens during free-space propagation.

Phase correlation becomes prominent as photons propagate.

Method enables high-dimensional quantum state analysis without references.

Abstract

With an extremely high dimensionality, the spatial degree of freedom of entangled photons is a key tool for quantum foundation and applied quantum techniques. To fully utilize the feature, the essential task is to experimentally characterize the multiphoton spatial wave function including the entangled amplitude and phase information at different evolutionary stages. However, there is no effective method to measure it. Quantum state tomography is costly, and quantum holography requires additional references. Here we introduce quantum Shack-Hartmann wavefront sensing to perform efficient and reference-free measurement of the biphoton spatial wave function. The joint probability distribution of photon pairs at the back focal plane of a microlens array is measured and used for amplitude extraction and phase reconstruction. In the experiment, we observe that the biphoton amplitude correlation becomes weak while phase correlation shows up during free-space propagation. Our work is a crucial step in quantum physical and adaptive optics and paves the way for characterizing quantum optical fields with high-order correlations or topological patterns.