Decoherence of Quantum Emitters in hexagonal Boron Nitride

TL;DR

This study investigates how common fabrication processes like annealing and doping affect the coherence of quantum emitters in hexagonal boron nitride, emphasizing the importance of minimal invasive techniques for quantum applications.

Contribution

It demonstrates that certain fabrication methods degrade coherence in hBN quantum emitters, while electron beam irradiation preserves coherence near the lifetime limit.

Findings

Annealing and doping cause decoherence via charge trap defects.

Electron beam irradiation maintains near-lifetime linewidths.

Crystal quality is crucial for coherent quantum emitters.

Abstract

Coherent quantum emitters are a central resource for advanced quantum technologies. Hexagonal boron nitride (hBN) hosts a range of quantum emitters that can be engineered using techniques such as high-temperature annealing, optical doping, and irradiation with electrons or ions. Here, we demonstrate that such processes can degrade the coherence, and hence the functionality, of quantum emitters in hBN. Specifically, we show that hBN annealing and doping methods that are used routinely in hBN nanofabrication protocols give rise to decoherence of B-center quantum emitters. The decoherence is characterized in detail, and attributed to defects that act as charge traps which fluctuate electrostatically during SPE excitation and induce spectral diffusion. The decoherence is minimal when the emitters are engineered by electron beam irradiation of as-grown, pristine flakes of hBN, where B-center linewidths approach the lifetime limit needed for quantum applications involving interference and entanglement. Our work highlights the critical importance of crystal lattice quality to achieving coherent quantum emitters in hBN, despite the common perception that the hBN lattice and hBN SPEs are highly-stable and resilient against chemical and thermal degradation. It underscores the need for nanofabrication techniques that are minimally invasive and avoid crystal damage when engineering hBN SPEs and devices for quantum-coherent technologies.