Coherent and Purcell-enhanced emission from erbium dopants in a cryogenic high-Q resonator

TL;DR

This paper demonstrates a cryogenic resonator system that significantly enhances erbium dopant emission while maintaining optical coherence, advancing quantum network node development.

Contribution

It introduces a high-Q cryogenic Fabry-Perot resonator integrating a thin erbium-doped crystal, achieving large emission enhancement without coherence loss.

Findings

59-fold emission rate enhancement

Purcell factor of 530

Lifetime-limited coherence up to 0.54 ms

Abstract

The stability and outstanding coherence of dopants and other atom-like defects in tailored host crystals make them a leading platform for the implementation of distributed quantum information processing and sensing in quantum networks. Albeit the required efficient light-matter coupling can be achieved via the integration into nanoscale resonators, in this approach the proximity of interfaces is detrimental to the coherence of even the least-sensitive emitters. Here, we establish an alternative: By integrating a 19 micrometer thin erbium-doped crystal into a cryogenic Fabry-Perot resonator with a quality factor of nine million, we can demonstrate 59(6)-fold enhancement of the emission rate, corresponding to a two-level Purcell factor of 530(50), while preserving lifetime-limited optical coherence up to 0.54(1) ms. With its emission at the minimal-loss wavelength of optical fibers and its outcoupling efficiency of 46(8) %, our system enables coherent and efficient nodes for long-distance quantum networks.