Review on coherent quantum emitters in hexagonal boron nitride

TL;DR

This review discusses optically coherent defect centers in hexagonal boron nitride, highlighting their potential for room-temperature quantum optics due to their unique layered structure and phonon decoupling.

Contribution

It provides a comprehensive overview of the current understanding, challenges, and future research directions for defect centers in hexagonal boron nitride.

Findings

Spectral linewidth remains narrow at room temperature.

Mechanically isolated orbitals protect coherence.

Potential applications in quantum photonics and spin optomechanics.

Abstract

Hexagonal boron nitride is an emerging two-dimensional material with far-reaching applications in fields like nanophotonics or nanomechanics. Its layered architecture plays a key role for new materials such as Van der Waals heterostructures. The layered structure has also unique implications for hosted, optically active defect centers. A very special type of defect center arises from the possibility to host mechanically isolated orbitals localized between the layers. The resulting absence of coupling to low-frequency acoustic phonons turns out to be the essential element to protect the coherence of optical transitions from mechanical interactions with the environment. Consequently, the spectral transition linewidth remains unusually narrow even at room temperature, thus paving a new way towards coherent quantum optics under ambient conditions. In this review, I summarize the state-of-the-art of defect centers in hexagonal boron nitride with a focus on optically coherent defect centers. I discuss the current understanding of the defect centers, remaining questions and potential research directions to overcome pervasive challenges. The field is put into a broad perspective with impact on quantum technology such as quantum optics, quantum photonics as well as spin optomechanics.