Overview of Photonic Crystal Cavities from Hexagonal Boron Nitride
This paper presents a significant advancement in the integration of hexagonal boron nitride (hBN) as a platform for scalable quantum photonic technologies. The researchers focus on the fabrication and tuning of photonic crystal cavities (PCCs) from hBN, emphasizing their potential use in integrated quantum photonics, polaritonics, and cavity quantum electrodynamics (QED) experiments.
Hexagonal boron nitride has attracted considerable attention due to its wide bandgap, hyperbolic optical properties, and ability to host ultra-bright, stable quantum emitters at room temperature. Despite these promising features, practical exploitation of hBN in on-chip nanophotonic circuits has been hindered by challenges related to the fabrication of high-quality monolithic optical resonators. This paper successfully addresses these challenges by demonstrating the fabrication of two-dimensional (2D) and one-dimensional (1D) photonic crystal cavities with optical quality (Q) factors exceeding 2,000.
Fabrication and Tuning Techniques
The researchers employed two main fabrication techniques: focused ion beam (FIB) milling and electron beam induced etching (EBIE). These methods were used to create suspended hBN cavities, leveraging hBN's layered structure and van der Waals forces that maintain the integrity of the stacked layers. The paper details the novel combination of reactive ion etching (RIE) and EBIE techniques to achieve nearly-straight sidewalls and precise cavity structures without significant degradation of the Q-factor.
A notable advancement highlighted in the paper is the iterative, deterministic tuning of cavity modes using EBIE, which allows for adjusting the resonant wavelength without requiring post-processing steps or causing substantial damage to the cavity. This method presents an advantageous approach for spectral tuning over a wide range, particularly valuable in matching the emission wavelengths of quantum emitters hosted by hBN.
Numerical Results and Implications
The fabrication techniques yielded 1D PCCs with Q-factors as high as 2,100, comparable to those found in bulk dielectric semiconductors such as diamond and SiC, which are known for hosting quantum emitters in the visible range. The high Q-factor is pivotal for applications in quantum photonics due to significant Purcell enhancement, facilitating strong light-matter interactions.
Additionally, the paper reports on the generation and spatial overlap of single photon emitters with cavity modes, achieved by annealing the hBN after fabrication. While spectral matching was not observed, the ability to create emitters within the cavity structure indicates potential for further integrated applications in quantum photonic circuits.
Future Directions
The techniques described in this paper pave the way for future research in developing deterministic methods for the fabrication of quantum emitters in hBN. Moreover, the demonstrated ability to tunably fabricate hBN resonators opens avenues for integrated on-chip quantum nanophotonics, optomechanics, and sensing technologies.
The paper also speculates on the possibility of using hBN in hybrid heterostructures with other 2D materials, offering novel opportunities for studies in light confinement and polaritonics. The extension of hBN's applicability to the mid and near-infrared ranges suggests promising developments in diverse fields requiring precise manipulation of light at the nanoscale.
Overall, this paper contributes to the evolving landscape of nanophotonics by presenting robust techniques for fabricating high-quality PCCs in hBN, setting a foundation for future explorations in quantum information processing and integrated photonic circuits.
