Determination of spatial quantum states by using Point Diffraction Interferometry

TL;DR

This paper introduces a method using point diffraction interferometry to efficiently reconstruct pure spatial qudits of any dimension, achieving high fidelity and robustness against turbulence in free-space quantum communication.

Contribution

The paper presents a novel interferometric scheme for reconstructing high-dimensional spatial quantum states with minimal measurements and demonstrates turbulence correction capabilities.

Findings

Achieved mean fidelity of 0.95 for 6-dimensional states.

Reconstructed quantum states with only four interferograms, independent of dimension.

Demonstrated correction of turbulence effects in free-space quantum communication.

Abstract

We present a method to reconstruct pure spatial qudits of arbitrary dimension $d$, which is based on a point diffraction interferometer. In the proposed scheme, the quantum states are codified in the discretized transverse position of a photon field, once they are sent through an aperture with $d$ slits, and a known background is added to provide a phase reference. To characterize these photonic quantum states, the complete phase wavefront is reconstructed through a phase-shifting technique. Combined with a multipixel detector, the acquisition can be parallelized, and only four interferograms are required to reconstruct any pure qudit, independently of the dimension $d$. We tested the method experimentally, for reconstructing states of dimension $d=6$ randomly chosen. A mean fidelity values of $0.95$ is obtained. Additionally, we develop an experimental scheme that allows to estimate phase aberrations affecting the wavefront upon propagation, and thus improve the quantum state estimation. In that regard, we present a proof-of-principle demonstration that shows the possibility to correct the influence of turbulence in a free-space communication, recovering mean fidelity values comparable to the propagation free of turbulence.