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Register a new userDemonstration of hybrid high-Q hexagonal boron nitride microresonators
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Hexagonal boron nitride (hBN) is a wide bandgap van der Waals material that is emerging as a powerful platform for quantum optics and nanophotonics. In this work, we demonstrate whispering gallery mode silica microresonators hybridized with thin layers of epitaxially grown hBN that exhibit high optical quality factor $> 7 times 10^5$. Measurements of the effect of hBN thickness on optical $Q$ and comparison with a theoretical model allows the linear optical absorption coefficient of the hBN films to be estimated. These high-$Q$ devices will be useful for applications in quantum and nonlinear optics, and their hybridized geometry provides a sensitive platform for evaluating losses in hBN and other 2D materials.
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Integration of solid state quantum emitters into nanophotonic circuits is a critical step towards fully on-chip quantum photonic based technologies. Among potential materials platforms, quantum emitters in hexagonal boron nitride have emerged over the last years as viable candidate. While the fundamental physical properties have been intensively studied over the last years, only few works have focused on the emitter integration into photonic resonators. Yet, for a potential quantum photonic material platform, the integration with nanophotonic cavities is an important cornerstone, as it enables the deliberate tuning of the spontaneous emission and the improved readout of distinct transitions for that quantum emitter. In this work, we demonstrate the resonant tuning of an integrated monolithic hBN quantum emitter in a photonic crystal cavity through gas condensation at cryogenic temperature. We resonantly coupled the zero phonon line of the emitter to a cavity mode and demonstrate emission enhancement and lifetime reduction, with an estimation for the Purcell factor of ~ 15.
Hexagonal boron nitride (h-BN), one of the hallmark van der Waals (vdW) layered crystals with an ensemble of attractive physical properties, is playing increasingly important roles in exploring two-dimensional (2D) electronics, photonics, mechanics, and emerging quantum engineering. Here, we report on the demonstration of h-BN phononic crystal waveguides with designed pass and stop bands in the radio frequency (RF) range and controllable wave propagation and transmission, by harnessing arrays of coupled h-BN nanomechanical resonators with engineerable coupling strength. Experimental measurements validate that these phononic crystal waveguides confine and support 15 to 24 megahertz (MHz) wave propagation over 1.2 millimeters. Analogous to solid-state atomic crystal lattices, phononic bandgaps and dispersive behaviors have been observed and systematically investigated in the h-BN phononic waveguides. Guiding and manipulating acoustic waves on such additively integratable h-BN platform may facilitate multiphysical coupling and information transduction, and open up new opportunities for coherent on-chip signal processing and communication via emerging h-BN photonic and phononic devices.
Hexagonal boron nitride (hBN) is an emerging layered material that plays a key role in a variety of two-dimensional devices, and has potential applications in nanophotonics and nanomechanics. Here, we demonstrate the first cavity optomechanical system incorporating hBN. Nanomechanical resonators consisting of hBN beams with predicted thickness between 8 nm and 51 nm were fabricated using electron beam induced etching and positioned in the optical nearfield of silicon microdisk cavities. A 160 fm/$sqrt{text{Hz}}$ sensitivity to the hBN nanobeam motion is demonstrated, allowing observation of thermally driven mechanical resonances with frequencies between 1 and 23 MHz, and mechanical quality factors reaching 1100 at room temperature in high vacuum. In addition, the role of air damping is studied via pressure dependent measurements. Our results constitute an important step towards realizing integrated optomechanical circuits employing hBN.
Hexagonal boron nitride (hBN)-long-known as a thermally stable ceramic-is now available as atomically smooth, single-crystalline flakes, revolutionizing its use in optoelectronics. For nanophotonics, these flakes offer strong nonlinearities, hyperbolic dispersion, and single-photon emission, providing unique properties for optical and quantum-optical applications. For nanoelectronics, their pristine surfaces, chemical stability, and wide bandgap have made them the key substrate, encapsulant, and gate dielectric for two-dimensional electronic devices. However, while exploring these advantages, researchers have been restricted to flat flakes or those patterned with basic slits and holes, severely limiting advanced architectures. If freely varying flake profiles were possible, the hBN structure would present a powerful design parameter to further manipulate the flow of photons, electrons, and excitons in next-generation devices. Here, we demonstrate freeform nanostructuring of hBN by combining thermal scanning-probe lithography and reactive-ion etching to shape flakes with surprising fidelity. We leverage sub-nanometer height control and high spatial resolution to produce previously unattainable flake structures for a broad range of optoelectronic applications. For photonics, we fabricate microelements and show the straightforward transfer and integration of such elements by placing a spherical hBN microlens between two planar mirrors to obtain a stable, high-quality optical microcavity. We then decrease the patterning length scale to introduce Fourier surfaces for electrons, creating sophisticated, high-resolution landscapes in hBN, offering new possibilities for strain and band-structure engineering. These capabilities can advance the discovery and exploitation of emerging phenomena in hyperbolic metamaterials, polaritonics, twistronics, quantum materials, and 2D optoelectronic devices.
Quantum emitters in van der Waals (vdW) materials have attracted lots of attentions in recent years, and shown great potentials to be fabricated as quantum photonic nanodevices. Especially, the single photon emitter (SPE) in hexagonal boron nitride (hBN) emerges with the outstanding room-temperature quantum performances, whereas the ubiquitous blinking and bleaching restrict its practical applications and investigations critically. The bubble in vdW materials exhibits the stable structure and can modify the local bandgap by strains on nanoscale, which is supposed to have the ability to fix this photostability problem. Here we report a bubble-induced high-purity SPE in hBN under ambient conditions showing stable quantum-emitting performances, and no evidence of blinking and bleaching for one year. Remarkably, we observe the nontrivial successive activating and quenching dynamical process of the fluorescent defects at the SPE region under low pressures for the first time, and the robust recoverability of the SPE after turning back to the atmospheric pressure. The pressure-tuned performance indicates the SPE origins from the lattice defect isolated and activated by the local strain induced from the bubble, and sheds lights on the future high-performance quantum sources based on hBN.
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