# Temporal Coherence of Single Photons Emitted by Hexagonal Boron Nitride Defects at Room Temperature

## TL;DR

This study examines the coherence of single photons from hBN defects at room temperature, finding that phonon dephasing limits their usefulness for quantum applications.

## Contribution

The paper reports the coherence time of hBN defect photons at room temperature using Michelson interferometry and phonon coupling analysis.

## Key findings

- The coherence time of hBN defect photons is limited by phonon dephasing processes.
- Phonon dephasing is 4 orders of magnitude faster than the emitter's spontaneous decay time.
- Strong electron-phonon coupling suggests cryogenic conditions are needed for quantum photonic applications.

## Abstract

Color centers in hexagonal boron nitride (hBN) emerge
as promising
quantum light sources at room temperature, with potential applications
in quantum communications, among others. The temporal coherence of
emitted photons (i.e., their capacity to interfere and distribute
photonic entanglement) is essential for many of these applications.
Hence, it is crucial to study and determine the temporal coherence
of this emission under different experimental conditions. In this
work, we report the coherence time of the single photons emitted by
an hBN defect in a nanocrystal at room temperature, measured via Michelson
interferometry. The visibility of this interference vanishes when
the temporal delay between the interferometer arms is a few hundred
femtoseconds, highlighting that the phonon dephasing processes are
4 orders of magnitude faster than the spontaneous decay time of the
emitter. We also analyze the single photon characteristics of the
emission via correlation measurements, defect blinking dynamics, and
its Debye–Waller factor. Our room temperature results highlight
the presence of a strong electron–phonon coupling, suggesting
the need to work at cryogenic temperatures to enable quantum photonic
applications based on photon interference.