Generation of Narrow-Band Polarization-Entangled Photon Pairs for Atomic Quantum Memories

TL;DR

This paper demonstrates a narrow-band polarization-entangled photon source with a linewidth suitable for atomic quantum memories, achieving high fidelity and long coherence length through cavity-enhanced spontaneous parametric down-conversion.

Contribution

The work presents the first experimental realization of a narrow-band, cavity-enhanced entangled photon source optimized for atomic quantum memories with high fidelity.

Findings

Linewidth of 9.6 MHz suitable for atomic memories

Fidelity of 94% in quantum state tomography

Coherence length of 32 meters measured

Abstract

We report an experimental realization of a narrow-band polarization-entangled photon source with a linewidth of 9.6 MHz through cavity-enhanced spontaneous parametric down-conversion. This linewidth is comparable to the typical linewidth of atomic ensemble based quantum memories. Single-mode output is realized by setting a reasonable cavity length difference between different polarizations, using of temperature controlled etalons and actively stabilizing the cavity. The entangled property is characterized with quantum state tomography, giving a fidelity of 94% between our state and a maximally entangled state. The coherence length is directly measured to be 32 m through two-photon interference.