Monolithic Polarizing Circular Dielectric Gratings on Bulk Substrates for Improved Photon Collection from InAs Quantum Dots

III-V semiconductor quantum dots (QDs) are near-ideal and versatile single-photon sources. Because of the capacity for monolithic integration with photonic structures as well as optoelectronic and optomechanical systems, they are proving useful in an increasingly broad application space. Here, we develop monolithic circular dielectric gratings on bulk substrates -- as opposed to suspended or wafer-bonded substrates -- for greatly improved photon collection from InAs quantum dots. The structures utilize a unique two-tiered distributed Bragg reflector (DBR) structure for vertical electric field confinement over a broad angular range. Opposing ``openings" in the cavities induce strongly polarized QD luminescence without harming collection efficiencies. We describe how measured enhancements depend critically on the choice of collection optics. This is important to consider when evaluating the performance of any photonic structure that concentrates farfield emission intensity. Our cavity designs are useful for integrating QDs with other quantum systems that require bulk substrates, such as surface acoustic wave phonons

Unidirectional luminescence from InGaN/GaN quantum-well metasurfaces

III-Nitride light emitting diodes (LEDs) are the backbone of ubiquitous lighting and display applications. Imparting directional emission is an essential requirement for many LED implementations. Although optical packaging, nano-patterning and surface roughening techniques can enhance LED extraction, directing the emitted light requires bulky optical components. Optical metasurfaces provide precise control over transmitted and reflected waveforms, suggesting a new route for directing light emission. However, it is difficult to adapt metasurface concepts for incoherent light emission, due to the lack of a phase-locking incident wave. In this Letter, we demonstrate metasurface-based design of InGaN/GaN quantum-well structures that generate narrow, unidirectional transmission and emission lobes at arbitrary engineered angles. We show that the directions and polarization of emission differ significantly from transmission, in agreement with an analytical Local Density of Optical States (LDOS) model. The results presented in this Letter open a new paradigm for exploiting metasurface functionality in light emitting devices

Tightly Confined Surface Acoustic Waves as Microwave-to-Optical Transduction Platforms in the Quantum Regime

Surface acoustic waves (SAWs) coupled to quantum dots (QDs), trapped atoms and ions, and point defects have been proposed as quantum transduction platforms, yet the requisite coupling rates and cavity lifetimes have not been experimentally established. Although the interaction mechanism varies, small acoustic cavities with large zero-point motion are required for high efficiencies. We experimentally demonstrate the feasibility of this platform through electro- and opto-mechanical characterization of tightly focusing, single-mode Gaussian SAW cavities at ~3.6 GHz on GaAs in the quantum regime, with mode volumes approaching 6{\lambda}^3. Employing strain-coupled single InAs QDs as optomechanical intermediaries, we measure single-phonon optomechanical coupling rates g_0 > 2{\pi} x 1 MHz, implying zero-point displacements >1 fm. In semi-planar cavities, we obtain quality factors >18,000 and finesse >140. To demonstrate operation at mK temperatures required for quantum transduction, we use a fiber-based confocal microscope in a dilution refrigerator to perform single-QD resonance fluorescence sideband spectroscopy showing conversion of microwave phonons to optical photons with sub-natural linewidths. These devices approach or meet the limits required for microwave-to-optical quantum transduction.Comment: 15 pages, 10 figure