Generation of subnatural-linewidth orbital angular momentum entangled biphotons using a single driving laser in hot atoms

TL;DR

This paper presents a novel, simplified method to generate narrow-bandwidth, orbital angular momentum entangled photon pairs using a single laser in hot rubidium vapor, achieving high fidelity and subnatural linewidths.

Contribution

It introduces the first demonstration of subnatural-linewidth OAM entangled biphotons in hot atomic vapor using a single driving laser, simplifying previous complex schemes.

Findings

Photon pairs have a linewidth of 4 MHz.

Quantum state tomography shows 95.7% fidelity.

Cross-correlation function reaches 27.7.

Abstract

Orbital angular momentum (OAM) entangled photon pairs with narrow bandwidths play a crucial role in the interaction of light and quantum states of matter. In this article, we demonstrate an approach for generating OAM entangled photon pairs with a narrow bandwidth by using a single driving beam in a $^{85}$Rb atomic vapor cell. This single driving beam is able to simultaneously couple two atomic transitions and directly generate OAM entangled biphotons by leveraging the OAM conservation law through the spontaneous four-wave mixing (SFWM) process. The photon pairs exhibit a maximum cross-correlation function value of 27.7 and a linewidth of 4 MHz. The OAM entanglement is confirmed through quantum state tomography, revealing a fidelity of 95.7\% and a concurrence of 0.926 when compared to the maximally entangled state. Our scheme is notably simpler than previously proposed schemes and represents the first demonstration of generating subnatural-linewidth entangled photon pairs in hot atomic systems.