A compact platform to integrate emitters in a cavity-like support is to embed quantum dots (QDs) in a photonic crystal (PhC) structure, making them promising candidates for integrated quantum photonic circuits. The emission properties of QDs can be modified by tailored photonic structures, relying on the Purcell effect or strong light-matter interactions. However, the effects of photonic states on spatial features of exciton emissions in these systems are rarely explored. Such effect is difficult to access due to random positions of self-assembled QDs in PhC structures, and the fact that quantum well excitons' wavefunctions resemble photonic states in a conventional distributed Bragg reflector cavity system. In this work, we instead observe a spatial signature of exciton emission using site-controlled QDs embedded in PhC cavities. In particular, we observe the detuning-dependent spatial repulsion of the QD exciton emissions by polarized imaging of the micro-photoluminescence, dependent on the controlled QD's position in a spatially extended photonic pattern. The observed effect arises due to the quantum interference between QD decay channel in a spatially-extended cavity mode. Our findings suggest that integration of site-controlled QDs in tailored photonic structures can enable spatially distributed single-photon sources and photon switches.

InGaAs/GaAs quantum dots (QDs) embedded in a GaAs substrate are very useful photon sources, including single and entangled photons, due to their unperturbed environment. Contrary to self-formed QDs, those grown in pyramidal pits can be well controlled in position and energy, important properties for scaling. However, photon extraction efficiency from these QDs is limited due to the GaAs/Air index mismatch and non-directionality of the emission. GaAs nanowires grown vertically on top of these QDs can serve as resonant antennas, thus enhancing their emission and increasing their usefulness as sources. Such structures were fabricated and their photon emission was studied by micro-photoluminescence as function of excitation power and temperature. The structures showed an intensity increase by up to x36 over quantum dots without nanowire antennas.

Emission properties of quantum light source can be modified through tailored photonic cavities via Purcell effect or strong light-matter interactions with various applications in integrated quantum photonics. The interacting excitonic and photonic states are core elements in the framework of cavity quantum electrodynamics. Successful characterization of subwavelength features of photonic modes from photonic crystal cavities constitutes basic building blocks for engineering the quantum photonic circuits. Potential trapping of polaritonic states has made great progress towards realizing efficient polaritonic devices. However, spatially features of excitonic states are rarely explored because extended wavefunction of quantum well excitons in the conventional quantum well – distributed Bragg reflector cavity system cannot be spatially distinguished from the photonic states. In this work, interactions of site-controlled quantum dots with a high-order cavity mode of an L7-type photonic crystal cavity with extended photonic states are spatially- and spectrally-resolved. We observed the first detuning-dependent spatial avoided crossing of the exciton-polaritons by polarized-imaging of the microphotoluminescence. Interestingly, such phenomenon is observed to be dependent on the position of the quantum dot in the cavity, with our precise control of the four quantum dot sites in the microcavity. The observed effect arises due to a unique quantum interference feature and can facilitate a deeper understanding of the spatial extent of a localized strongly-coupled excitonic state interacting with an extended photonic mode pattern. Based on our results, incorporating site-controlled quantum dots at prescribed locations in a photonic structure with tailored spatial patterns of photonic states can enable new integrated photonic devices with functionalities such as single-photon transport to remote locations for quantum information processing, quantum engineering, and quantum metrology.

Interactions of site-controlled quantum dots with a high-order cavity mode of an $L7$ -type photonic crystal cavity are resolved spatially and spectrally. We observed a spatial avoided crossing in polarization-resolved optical emission of quantum dots.

Precise positioning of single site-controlled inverted pyramidal InGaAs QD at the antinode of a GaAs photonic crystal cavity with nanometer-scale accuracy holds unique advantages compared to self-assembled QDs and offers great promise for practical on-chip photonic quantum information processing. However, the strong coupling regime in this geometry has not yet been achieved due to the low cavity Q-factor based on the (111)B-oriented membrane structures. Here, we reveal the onset of phonon-mediated coherent exciton-photon interaction on our tailored single site-controlled InGaAs QD - photonic crystal cavity. Our results present a Rabi-like oscillation of luminescence intensity between excitonic and photonic components correlated with their energy splitting pronounced at small detuning. Such Rabi-like oscillation is well reproduced by modeling the coherent exchange of the exciton-photon population. The modeling further reveals an oscillatory two-time covariance at QD-cavity resonance, which indicates that the system operates at the onset of the strong coupling regime. Moreover, by using the cavity mode as a probe of the virtual state of the QD induced by phonon scattering, it reveals an increase in phonon scattering rates near the QD-cavity resonance and asymmetric phonon emission and absorption rate even around 50 K.

Deterministic positioning single site-controlled high symmetric InGaAs quantum dots (QDs) in (111)B-oriented GaAs photonic crystal cavities with nanometer-scale accuracy provides an idea component for building integrated quantum photonic circuits. However, it has been a long-standing challenge of improving cavity Q-factors in such systems. Here, by optimizing the trade-off between the cavity loss and QD spectral quality, we demonstrate our site-controlled QD-nanocavity system operating in the intermediate coupling regime mediated by phonon scattering, with the dynamic coexistence of strong and weak coupling. The cavity-exciton detuning-dependent micro-photoluminescence spectrum reveals concurrence of a trend of exciton-polariton mode avoided crossing, as a signature of Rabi doublet of the strongly coupled system. Meanwhile, a trend of keeping constant or slight blue shift of coupled exciton–cavity mode(CM) energy across zero-detuning is ascribed to the formation of collective states mediated by phonon-assisted coupling, and their rare partial out-of-synchronization linewidth-narrowing is linked to their coexisting strong-weak coupling regime. We further reveal the pump power-dependent anti-bunching photon statistical dynamics of this coexisting strong-weak coupled system and the optical features of strongly confined exciton-polaritons, and dark-exciton-like states. These observations demonstrate the potential capabilities of site-controlled QD-cavity systems as deterministic quantum nodes for on-chip quantum information processing and provide guidelines for future device optimization for achieving the strong coupling regime.

We demonstrate the on-chip photon routing on a site-controlled quantum dots embedded W1 photonic crystal waveguides side coupled to a L3 cavity. Observed photon propagation through the device indicates the connectivity of all photonic elements.

We demonstrate high-resolution cryogenic photoluminescence measurements on exciton complexes emitting ≈ 1 μm of a single-site-controlled highly-symmetric quantum dot-nanocavity system. Observed fine spectral features uncover the C 3v QD symmetry and cavity quantum electrodynamics.

Precise positioning of single quantum dots (QDs) in photonics crystal (PhC) cavities with nanometer-scale accuracy offers great promise for on-chip integrated quantum photonic circuit. In such coupled QD-cavity system, the decoherence fundamentally affects the coherent control for quantum communication and information processing. However, accessing to the strong-coupling regime and the impact of pure dephasing in such system have been rarely reported yet. Here, relying on our unique site-controlled pyramidal InGaAs/GaAs QDs – high-Q-PhC cavities platform, we investigate the cavity quantum electrodynamics towards strong-coupling regime mediated by pure dephasing. We demonstrate the anti-crossing and mutual linewidth narrowing of the single excitonic emission strongly coupled to cavity mode near resonance. We further present the signatures of Rabi-like oscillation and quantum beating between upper and lower branch of polariton.

We demonstrate the cavity quantum electrodynamics towards strong-coupling regime mediated by cavity loss and exciton pure dephasing in singular site-controlled quantum dotnanocavity system, studied by micro-photoluminescence (µ-PL) and time-resolved PL (TRPL).

We demonstrate the controllable exciton-cavity mode interaction mediated by pure dephasing in a single site-controlled quantum dot-nanocavity system. With varying detuning, Purcell enhanced dynamics and phonon-assisted cavity feeding sequentially dominate the exciton-cavity mode interaction.

Remote coupling between quantum emitters is of great importance for constructing quantum networks. Conventionally, this can be achieved via photon exchange by incorporating the quantum emitters in a waveguide or a large cavity. However, such photonic structures suffer from low quality-factors or large mode volumes, limiting the efficiency of light–matter interaction. Here, we demonstrate remote coupling between two site-controlled semiconductor quantum dot emitters mediated by an optical Fano resonance induced by coupling cavity modes via a continuum waveguide state. Unlike ordinary coupled modes, the Fano mode offers both a spatially extended field and a high local density of optical states at the emitters, enhancing light–matter interaction. This coupling scheme allows the demonstration of mutual excitation between two quantum dots separated in space by > 17 wavelengths. Our approach holds promise for achieving long-distance interaction without compromising interaction efficiency, which is essential for scaling up on-chip integration of quantum networks based on solid-state quantum emitters.

We investigate the exciton complexes photoluminescence, dynamics and photon statistics in the concurrent strong weak coupling regime in our unique site controlled singular inverted pyramidal InGaAs/GaAs quantum dots photonic crystal cavities platform. Different from a clear boundary between strong and weak QD cavity coupling, we demonstrate the strong and weak coupling can coexist dynamically, as a form of intermediate regime mediated by phonon scattering. The detuning dependent microphotoluminescence spectrum reveals concurrence of exciton cavity polariton mode avoided crossing, as a signature of Rabi doublet of the strong coupled system, the blue shifting of coupled exciton cavity mode energy near zero detuning ascribed to the formation of collective states mediated by phonon assisted coupling, and their partial out of synchronization linewidth narrowing linked to their mixed behavior. By detailing the optical features of strongly confined exciton-photon complexes and the quantum statistics of coupled cavity photons, we reveal the dynamics and antibunching/bunching photon statistical signatures of the concurrent strong weak intermediate coupled system at near zero-detuning. This study suggests our device has potential for new and subtle cavity quantum electrodynamical phenomena, cavity enhanced indistinguishable single photon generation, and cluster state generation via the exciton-photon complexes for quantum networks.

We investigate a photonic crystal structure where distant, identical nanocavities incorporating site-controlled semiconductor quantum dots are coupled with a bus waveguide. We show that the cavities can be resonant frequency matched even upon fabrication imperfection.

We demonstrate the fabrication of arrayed, site-controlled pyramidal InGaAs/GaAs quantum dots (QDs) grown by metalorganic vapor phase epitaxy with tailored emission energy and periods as small as 200 nm, suitable for the integration with compact photonic structures. The observed variation of the QD emission energy with the geometric parameters of the array is attributed to adatom and precursor diffusion mechanisms during epitaxial growth. By adjusting the pattern geometry, the emission energy can be tuned over a wide range of ∼80 meV around 1.4 eV, with inhomogeneous broadening <10 meV. Single photon emission of isolated QDs with gX,X(2)(0)=0.11 is demonstrated, which attests to the suitability of these QDs for nanophotonic applications.

Growth of InGaAs/GaAs quantum dots (QDs) in inverted pyramids on pre-patterned {111}B GaAs substrates is a versatile technique allowing for precise site and emission energy control. We report on the fabrication of QDs with a wavelength setting within a range of 100 meV achieved in a single growth step by varying the pyramid size and without compromising the optical quality. Low-temperature micro-photoluminescence spectra of the QD ensembles exhibit low inhomogeneous broadening (similar to 15 meV) and excitonic linewidths as low as 50 eV. Moreover, we demonstrate the selective energy tuning of a single QD embedded within an ensemble of QDs spectrally blue-shifted by as much as 40 meV, which is of interest for single QD spectroscopy and the fabrication of integrated multi-wavelength single photon sources.

We demonstrate the self-formation of hexagonal nanotemplates on GaAs (111)B substrates patterned with arrays of inverted tetrahedral pyramids during metal-organic vapor phase epitaxy and its role in producing high-symmetry, site-controlled quantum dots (QDs). By combining atomic force microscopy measurements on progressively thicker GaAs epitaxial layers with kinetic Monte Carlo growth simulations, we demonstrate self-maintained symmetry elevation of the QD formation sites from three-fold to six-fold symmetry. This symmetry elevation stems from adatom fluxes directed towards the high-curvature sites of the template, resulting in the formation of a fully three-dimensional hexagonal template after the deposition of relatively thin GaAs layers. We identified the growth conditions for consistently achieving a hexagonal pyramid bottom, which are useful for producing high-symmetry QDs for efficient generation of entangled photons.

Rectangular arrays of pyramidal recesses coated by silver film are investigated by means of polarization-resolved nonlinear microscopy at 900 nm fundamental wavelength, demonstrating strong dependence of the dipole-allowed SHG upon the lattice parameters. The plasmonic band gap causes nearly complete SHG suppression in arrays of 650 nm periodicity, whereas a sharp resonance at 550 nm periodicity is observed due to excitation of band edge Bloch states at fundamental frequency, accompanied by symmetry-constrained interactions with similar modes at the second-harmonic frequency. Additionally, coupling with modes at the bottom side of the silver film may lead to extraordinary optical transmission, opening a channel for SHG from the highly nonlinear GaAs substrate. Changing the lattice geometry enables SHG intensity modulation over three orders of magnitude, while the effective nonlinear anisotropy can be continuously switched between the two lattice directions, reaching values as high as +/- 0.96.

We report on the effects of optical disorder on breaking the symmetry of the cavity modes of H3 photonic crystal cavities incorporating site-controlled pyramidal quantum dots (QDs) as the internal light source. The high in-plane symmetry of the polarization states of the pyramidal QDs simplifies the analysis of the polarization states of the H3 cavities. It is shown that the optical disorder induced by fabrication imperfections lifts the degeneracy of the two quadrupole cavity modes and tilts the elongation axes of the cavity mode patterns with respect to the ideal, hexagonal symmetry case. These results are useful for designing QD-cavity structures for polarization-entangled photon sources and few-QD lasers.