4:30 PM - *EQ01.07.03
Coherence Properties of Quantum Emitters in hBN
Mehran Kianinia1,Simon White1,Milos Toth1,Igor Aharonovich1
University of Technology Sydney1
Solid state quantum light sources are emerging as promising candidates for many applications in quantum technologies [1-3]. Among these sources, optically active point defects in hexagonal boron nitride (hBN) are attracting considerable attention due to their extreme brightness, and high Debye Waller factor which means the majority of the photons are emitted into the zero phonon line (ZPL) . While final defect assignments are still under debate , a number of recent experiments and theoretical papers hint at carbon related defects adjacent to a vacancy site in the hBN lattice [4,5]. In addition, numerous recent studies have shown that several defects in hBN exhibit spin dependent optical transitions, and exhibit optically detected magnetic resonance (ODMR), which is vital for their employment as solid state qubits and quantum sensors at the nano-scale [6,7].
For practical quantum photonic applications, where photon interference and generations of indistinguishable photons are required , it is important to characterize the coherent properties of the emitted photons. Specifically, studies of dephasing mechanisms, coherence and line broadening effects underpin the applicability of quantum emitters for photon interference experiments. Previous studies of hBN quantum emitters have revealed the emissions in hBN are broadly affected by spectral diffusion. Preliminary resonant excitation experiments showed that observation of Fourier Transform limited lines is possible, but rather rare, as compared to other solid state emitters, such as diamond [28,29]. Some of the challenges stemmed from the fact that the level structure of the emitters is still poorly understood, and environmental effects in layered materials are strongly sample-dependent.
In this presentation, we will report on spectroscopy of hBN defects at cryogenic temperature to study dephasing mechanism of quantum emitters in details. Importantly, our work focuses predominantly on coherent excitation (i.e. the excitation laser is on-resonance with the hBN emission). First we characterize the significant dephasing and spectral broadening mechanisms in an hBN single photon emitter under resonant excitation. We find that the resonant linewidth, even at cryogenic temperature, is dominated by phonon broadening and results in linewidths of ~ 1 GHz. We also see that degenerate electronic states and strain do not play a significant role in phonon dephasing. We further showed that spectral diffusion can be minimized by employing excitation powers well below saturation. Overall, the brightness of the emitters exemplify that emission rate in excess of 200 MHz with bandwidth of less than 1 GHz . Next we employed a weak non-resonant laser at a wavelength between 500 nm and 532 nm, in addition to the resonant laser that drives the system coherently to stabilise the optical transition of single defects in hBN. The secondary laser acts as an additional excitation pathway and re-initializes the system into its bright state. The two laser repumping scheme enables the observation of brighter resonant fluorescence . We provide an in-depth analysis of the photodynamics of the system, and discuss its applicability for an improved coherence. Our results provide an important analysis and required modification for future experiments on two photon interference with quantum emitters in hBN.
 I. Aharonovich, et al., Nat. Photonics 10, 631-641, (2016).
 A. W. Elshaari, et al., Nat. Photonics, (2020).
 M. Atatüre, et al., Nature Reviews Materials 3, 38-51, (2018).
 N. Mendelson, et al, Nature Materials 20, 321-328, (2021).
 C. Jara, et al, The Journal of Physical Chemistry A 125, 1325-1335, (2021).
 A. Gottscholl, et al., Nature Mater. 19, 540-545, (2020).
 N. Chejanovsky, et al., Nature Materials, (2021).
 S. J. White, et al., https://arxiv.org/abs/2105.11687 (2021).
 S. J. U. White, et al., Physical Review Applied 14, 044017, (2020).