Lifetime-Limited and Tunable Quantum Light Emission in h-BN via Electric Field Modulation

Hexagonal Boron Nitride Based Photonic Quantum Technologies

Hexagonal boron nitride is rapidly gaining interest as a platform for photonic quantum technologies, due to its two-dimensional nature and its ability to host defects deep within its large band gap that may act as room-temperature single-photon emitters. In this review paper we provide an overview of (1) the structure, properties, growth and transfer of hexagonal boron nitride; (2) the creationof colour centres in hexagonal boron nitride and assignment of defects by comparison with ab initio calculations for applications in photonic quantum technologies; and (3) heterostructure devices for the electrical tuning and charge control of colour centres that form the basis for photonic quantum technology devices. The aim of this review is to provide readers a summary of progress in both defect engineering and device fabrication in hexagonal boron nitride based photonic quantum technologies.

Carbon-Related Quantum Emitter in Hexagonal Boron Nitride with Homogeneous Energy and 3-Fold Polarization

Most hexagonal boron nitride (hBN) single-photon emitters (SPEs) studied to date suffer from variable emission energy and unpredictable polarization, two crucial obstacles to their application in quantum technologies. Here, we report an SPE in hBN with an energy of 2.2444 ± 0.0013 eV created via carbon implantation that exhibits a small inhomogeneity of the emission energy. Polarization-resolved measurements reveal aligned absorption and emission dipole orientations with a 3-fold distribution, which follows the crystal symmetry. Photoluminescence excitation (PLE) spectroscopy results show the predictability of polarization is associated with a reproducible PLE band, in contrast with the non-reproducible bands found in previous hBN SPE species. Photon correlation measurements are consistent with a three-level model with weak coupling to a shelving state. Our ab initio excited-state calculations shed light on the atomic origin of this SPE defect, which consists of a pair of substitutional carbon atoms located at boron and nitrogen sites separated by a hexagonal unit cell.

Electrical tuning of quantum light emitters in hBN for free space and telecom optical bands

Quantum light emitters (also known as single photon emitters) are known to be the heart of quantum information technologies. Irrespective of possessing ideal single photon emitter properties, quantum emitters in 2-D hBN defect structures, exhibit constrained quantum light emission within the 300-700 nm range. However, this emission range cannot fully satisfy the needs of an efficient quantum communication applications such as quantum key distribution (QKD), which demands the quantum light emission in fiber optic telecom wavelength bands (from 1260 to 1625 nm) and the free space optical (FSO) (UV-C-solar blind band-100 to 280 nm) wavelength ranges. Hence, there is a necessity to tune the quantum light emission into these two bands. However, the most promising technique to tune the quantum light emitters in hBN here, is still a matter of debate and till date there is no experimental and theoretical assurances. Hence, this work will focus on one of the most promising simple techniques known as Stark electrical tuning of the quantum light emission of hBN defect structures (NBVN, VB, CB, CBVN, CBCN, CBCNCBCN complex, and VBO2). These hBN defects are designed and sandwiched as metal/graphene/hBN defect structure/graphene/metal heterostructure and electrically tuned towards FSO and fiber optic bands (tuning range from UV-C to O-band IR region) region, using constrained DFT computations. The external electric field predicted to yield an atomic bond angle tilt associated with this point defect structure creates out-of-plane dipole moments, enabling the tuning of quantum emission. This electrical tuning technique leads to a simple passive photonic component which enables easier compatibility with quantum circuits and it is found to be one of the perfect alternative solutions, which does not require much external hardware setup to implement as compared to earlier published strain induced tuning experiments.

Time-dependent Mandel Q parameter analysis for a hexagonal boron nitride single photon source

The time-dependent Mandel Q parameter, Q(T), provides a measure of photon number variance for a light source as a function of integration time. Here, we use Q(T) to characterise single photon emission from a quantum emitter in hexagonal boron nitride (hBN). Under pulsed excitation a negative Q parameter was measured, indicating photon antibunching at an integration time of 100 ns. For larger integration times Q is positive and the photon statistics become super-Poissonian, and we show by comparison with a Monte Carlo simulation for a three-level emitter that this is consistent with the effect of a metastable shelving state. Looking towards technological applications for hBN single photon sources, we propose that Q(T) provides valuable information on the intensity stability of single photon emission. This is useful in addition to the commonly used g⁽²⁾(τ) function for the complete characterisation of a hBN emitter.

Quantum Emitters in Hexagonal Boron Nitride

Hexagonal boron nitride (hBN) has emerged as a fascinating platform to explore quantum emitters and their applications. Beyond being a wide-bandgap material, it is also a van der Waals crystal, enabling direct exfoliation of atomically thin layers─a combination which offers unique advantages over bulk, 3D crystals. In this Mini Review we discuss the unique properties of hBN quantum emitters and highlight progress toward their future implementation in practical devices. We focus on engineering and integration of the emitters with scalable photonic resonators. We also highlight recently discovered spin defects in hBN and discuss their potential utility for quantum sensing. All in all, hBN has become a front runner in explorations of solid-state quantum science with promising future prospects.