Radial Bragg gratings are commonly used to enhance light extraction from quantum emitters, but lack a well-suited, fast simulation method for optimization beyond periodic designs. To overcome this limitation, an algorithm based on the transfer matrix model (TMM) to calculate the free-space emission of such gratings is proposed and demonstrated. Using finite difference time domain (FDTD) simulations, free-space emission, and transfer matrices of single grating components are characterized. The TMM then combines any number of components to receive the total emission. Randomized benchmarks verify that results from this method agree within 98% with FDTD while reducing simulation time by one to two orders of magnitude. The speed advantage of this approach is shown by maximizing emission of a fifteen-trench circular grating into a Gaussian mode. It is expected that this novel algorithm will facilitate the optimization of radial gratings, enabling quantum light sources with unprecedented collection efficiencies. Using finite difference time domain (FDTD) simulations, free-space emission and transfer matrices of single radial grating components are characterized. The transfer matrix model introduced here then combines any number of components to receive the total emission of the radial grating. Benchmarks show 98% agreement with FDTD but 10- to 100-fold speed advantage, allowing efficient optimization of aperiodic radial grating designs.image

Group IV vacancy color centers in diamond are promising spin-photon interfaces with strong potential for applications in photonic quantum technologies. Reliable methods for controlling and stabilizing their charge state are urgently needed for scaling to multiqubit devices. Here, we manipulate the charge state of silicon vacancy (SiV) ensembles by combining luminescence and photocurrent spectroscopy. We controllably convert the charge state between the optically active SiV- and dark SiV2- with megahertz rates and >90% contrast by judiciously choosing the local potential applied to in-plane surface electrodes and the laser excitation wavelength. We observe intense SiV- photoluminescence under hole capture, measure the intrinsic conversion time from the dark SiV2- to the bright SiV- to be 36.4(67) ms, and demonstrate how it can be enhanced by a factor of 105 via optical pumping. Moreover, we obtain previously unknown information on the defects that contribute to photoconductivity, indicating the presence of substitutional nitrogen and divacancies.

We report lasing of moiré trapped interlayer excitons (IXs) by integrating a pristine hBN-encapsulated MoSe2/WSe2 heterobilayer into a high-Q (>10(4)) nanophotonic cavity. We control the cavity-IX detuning using a magnetic field and measure their dipolar coupling strength to be 78 +/- 4 micro-electron volts, fully consistent with the 82 micro-electron volts predicted by theory. The emission from the cavity mode shows clear threshold-like behavior as the transition is tuned into resonance with the cavity. We observe a superlinear power dependence accompanied by a narrowing of the linewidth as the distinct features of lasing. The onset and prominence of these threshold-like behaviors are pronounced at resonance while weak off-resonance. Our results show that a lasing transition can be induced in interacting moiré IXs with macroscopic coherence extending over the length scale of the cavity mode. Such systems raise interesting perspectives for low-power switching and synaptic nanophotonic devices using two-dimensional materials.

Janus transition metal dichalcogenides are an emerging class of atomically thin materials with engineered broken mirror symmetry that gives rise to long-lived dipolar excitons, Rashba splitting, and topologically protected solitons. They hold great promise as a versatile nonlinear optical platform due to their broadband harmonic generation tunability, ease of integration on photonic structures, and nonlinearities beyond the basal crystal plane. Here, second and third harmonic generation in MoSSe and WSSe Janus monolayers is studied. Polarization-resolved spectroscopy is used to map the full second-order susceptibility tensor of MoSSe, including its out-of-plane components. In addition, the effective third-order susceptibility and the second-order nonlinear dispersion close to exciton resonances for both MoSSe and WSSe are measured at room and cryogenic temperatures. This work sets a bedrock for understanding the nonlinear optical properties of Janus transition metal dichalcogenides and probing their use in the next-generation on-chip multifaceted photonic devices.

In recent years, there has been a significant increase in interest in tuning the emission wavelength of InAs quantum dots (QDs) to wavelengths compatible with the already existing silica fiber networks. In this work, we develop and explore compositionally graded In x Ga 1-x As metamorphic buffer layers (MBLs), with lattice constant carefully tailored to tune the emission wavelengths of InAs QDs towards the telecom O-band. The designed heterostructure is grown by molecular beam epitaxy (MBE), where a single layer of InAs QDs is grown on top of the MBL and is capped with a layer having a fixed indium (In) content. We investigate the structural properties of the grown MBLs by reciprocal space mapping, as well as transmission electron microscopy, and verify the dependence of the absorption edge of the MBL on the In-content by photothermal deflection spectroscopy measurements. This allows us to identify a growth temperature range for which the MBLs achieve a near-equilibrium strain relaxation for In-content up to similar to 30 % . Furthermore, we explore the emission wavelength tunability of QDs grown on top of a residual strained layer with a low density of dislocations. Specifically, we demonstrate a characteristic red-shift of the QD photoluminescence towards the telecom O-band (1300 nm) at low temperature. This study provides insights into the relaxation profiles and dislocation propagation in compositionally graded MBLs grown via MBE thus paving the way for realizing MBE-grown heterostructures containing InAs QDs for advanced nanophotonic devices emitting in the telecom bands.

We report resonant Raman spectroscopy of neutral excitons X0 and intravalley trions X- in hBN-encapsulated MoS2 monolayer embedded in a nanobeam cavity. By temperature tuning the detuning between Raman modes of MoS2 lattice phonons and X0/X- emission peaks, we probe the mutual coupling of excitons, lattice phonons and cavity vibrational phonons. We observe an enhancement of X0-induced Raman scattering and a suppression for X--induced, and explain our findings as arising from the tripartite exciton-phonon-phonon coupling. The cavity vibrational phonons provide intermediate replica states of X0 for resonance conditions in the scattering of lattice phonons, thus enhancing the Raman intensity. In contrast, the tripartite coupling involving X- is found to be much weaker, an observation explained by the geometry-dependent polarity of the electron and hole deformation potentials. Our results indicate that phononic hybridization between lattice and nanomechanical modes plays a key role in the excitonic photophysics and light-matter interaction in 2D-material nanophotonic systems.

We demonstrate that semiconductor quantum dots can be excited efficiently in a resonant three-photon process, while resonant two-photon excitation is highly suppressed. Time-dependent Floquet theory is used to quantify the strength of the multiphoton processes and model the experimental results. The efficiency of these transitions can be drawn directly from parity considerations in the electron and hole wave functions in semiconductor quantum dots. Finally, we exploit this technique to probe intrinsic properties of InGaN quantum dots. In contrast to nonresonant excitation, slow relaxation of charge carriers is avoided, which allows us to measure directly the radiative lifetime of the lowest energy exciton states. Since the emission energy is detuned far from the resonant driving laser field, polarization filtering is not required and emission with a greater degree of linear polarization is observed compared to nonresonant excitation.

Optoelectronic properties of van der Waals homostructures can be selectively engineered by the relative twist angle between layers. Here, we study the twist-dependent moire ' coupling in MoSe2 homobilayers. For small angles, we find a pronounced redshift of the K -K and Gamma-K excitons accompanied by a transition from K -K to Gamma-K emission. Both effects can be traced back to the underlying moire ' pattern in the MoSe2 homobilayers, as confirmed by our low-energy continuum model for different moire ' excitons. We identify two distinct intralayer moire ' excitons for R stacking, while H stacking yields two degenerate intralayer excitons due to inversion symmetry. In both cases, bright interlayer excitons are found at higher energies. The performed calculations are in excellent agreement with experiment and allow us to characterize the observed exciton resonances, providing insight about the layer composition and relevant stacking configuration of different moire ' exciton species.

Atomically thin semiconductors can be readily integrated into a wide range of nanophotonic architectures for applications in quantum photonics and novel optoelectronic devices. We report the observation of nonlocal interactions of ???free??? trions in pristine hBN/MoS2/hBN heterostructures coupled to single mode (Q > 104) quasi 0D nanocavities. The high excitonic and photonic quality of the interaction system stems from our integrated nanofabrication approach simultaneously with the hBN encapsulation and the maximized local cavity field amplitude within the MoS2 monolayer. We observe a nonmonotonic temperature dependence of the cavity-trion interaction strength, consistent with the nonlocal light-matter interactions in which the extent of the center-of-mass (c.m.) wave function is comparable to the cavity mode volume in space. Our approach can be generalized to other optically active 2D materials, opening the way toward harnessing novel light-matter interaction regimes for applications in quantum photonics.