Temporal coherence of single photons emitted by hexagonal Boron Nitride defects at room temperature

TL;DR

This study measures the temporal coherence of single photons emitted by hBN defects at room temperature, revealing rapid phonon dephasing that impacts quantum photonic applications and emphasizing the need for cryogenic conditions.

Contribution

First measurement of the coherence time of single photons from hBN defects at room temperature using Michelson interferometry, highlighting phonon dephasing effects.

Findings

Interference visibility vanishes within a few hundred femtoseconds.

Phonon dephasing is four orders of magnitude faster than spontaneous emission.

Strong phonon-electron coupling observed in the emission characteristics.

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 four 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 phonon-electron coupling, suggesting the need to work at cryogenic temperatures to enable quantum photonic applications based on photon interference.