Measuring Qutrit-Qutrit Entanglement of Orbital Angular Momentum States of an Atomic Ensemble and a Photon

TL;DR

This paper demonstrates the creation and measurement of three-dimensional entanglement between an atomic ensemble and a photon using orbital angular momentum states, confirming genuine qutrit-qutrit entanglement.

Contribution

It reports the first full state tomography of atomic-photon qutrit entanglement and confirms high-fidelity entanglement with Schmidt rank 3, advancing quantum information processing.

Findings

Fidelity to maximally entangled state exceeds 2/3 threshold

Density matrix cannot be decomposed into lower Schmidt rank states

Schmidt number confirmed to be at least 3

Abstract

Three-dimensional entanglement of orbital angular momentum states of an atomic qutrit and a single photon qutrit has been observed. Their full state was reconstructed using quantum state tomography. The fidelity to the maximally entangled state of Schmidt rank 3 exceeds the threshold 2/3. This result confirms that the density matrix cannot be decomposed into ensemble of pure states of Schmidt rank 1 or 2. That is, the Schmidt number of the density matrix must be equal to or greater than 3.