Enhancement Of Emission Rate Research Articles

Cavity Quantum Electrodynamics with Second‐Order Topological Corner State

AbstractTopological photonics provides a new paradigm in studying cavity quantum electrodynamics with robustness to disorder. In this work, the coupling between single quantum dots and the second‐order topological corner state are demonstrated. Based on the second‐order topological corner state, a topological photonic crystal cavity is designed and fabricated into GaAs slabs with quantum dots embedded. The coexistence of corner state and edge state with high quality factor close to 2000 is observed. The enhancement of photoluminescence intensity and emission rate are both observed when the quantum dot is on resonance with the corner state. This result enables the application of topology into cavity quantum electrodynamics, offering an approach to topological devices for quantum information processing.

Broadband enhancement of light-matter interaction in photonic crystal cavities integrating site-controlled quantum dots

The fabrication of integrated quantum dot (QD)-optical microcavity systems is a requisite step for the realization of a wide range of nanophotonic experiments (and applications) that exploit the ability of QDs to emit nonclassical light, e.g., single photons. Thanks to their \ensuremath{\sim}20-nm positioning accuracy and to their proven potential for single-photon operation, the QDs obtained by spatially selective hydrogen irradiation of dilute-nitride semiconductors ---such as Ga(AsN) and Ga(PN)---are uniquely suited for integration with photonic nanodevices. In the present work, we demonstrate the ability to deterministically integrate single, site-controlled Ga(AsN)/Ga(AsN):H QDs within a photonic crystal (PhC) cavity. The properties of the fabricated QD-PhC cavity systems are then probed by photon correlation---providing clear evidence of single-photon emission---and time-resolved microphotoluminescence spectroscopy. Detailed information on the dynamics of our integrated nanodevices can be inferred by comparing these experiments to the solutions of a rate-equations system, developed by taking into account all the main processes leading to the capture, relaxation, and recombination of carriers in and out of the QD. This allows us to follow the evolution of the relevant recombination rates in our system for varying energy detuning, \ensuremath{\Delta}$E$, between the QD and the PhC cavity. When the QD exciton transition is nearly resonant with the cavity mode, a large (gtenfold) enhancement of the spontaneous emission rate is observed, in substantial agreement with Jaynes-Cummings (JC) theory. For intermediate detunings (\ensuremath{\Delta}$E$ \ensuremath{\sim} 1.5--3.5 meV), on the other hand, the observed enhancement is significantly larger than that predicted by JC theory, due to the important role played by acoustic phonons in mediating the QD-PhC cavity coupling in a solid-state environment. Apart from its fundamental interest, the observation of such phonon-mediated, broadband enhancement of light-matter interaction significantly relaxes the requirements for the realization of a large variety of cavity QED-based experiments and applications. These include many photonic devices for which the use of site-controlled Ga(AsN)/Ga(AsN):H QDs would be inherently advantageous, such as those based on the coupling between more than one QD and a single cavity mode (e.g., few-QD nanolasers and QD solids).

Charge-state conversion in nitrogen-vacancy centers mediated by an engineered photonic environment

The nitrogen-vacancy (NV) center in nanodiamonds has emerged as an excellent platform in quantum technologies due to its applications in spin manipulation and nanoscale sensing. However, their use is limited by the unavoidable charge-state conversion under optical pumping. In this study, we investigate the control of charge-state conversion in NV centers using an engineered photonic environment and thus change the available local density of optical states (LDOS). The spectral- and pump-dependent decay rate measurements are performed to study the redistribution of emission rates due to the change in LDOS and their effect on charge-state conversion. We have achieved an 8% enhancement of emission rate at the zero phonon line which is accompanied with a 10% suppression in the phonon sideband emission rate in the low-pump-power regime. In the high-pump-power regime, the charge-state conversion becomes inevitable and leads to the deterioration of LDOS-induced modification in the NV center emission lifetimes. The results are useful for efficient NV center spin readout and charge-state depletion microscopy utilizing reversible charge-state conversion.

Geometrically Tunable Beamed Light Emission from a Quantum‐Dot Ensemble Near a Gradient Metasurface

AbstractOptical metasurfaces have been widely investigated in recent years as a means to tailor the wavefronts of externally incident light for passive device applications. At the same time, their use in active optoelectronic devices such as light emitters is far less established. This work explores their ability to control the radiation properties of a nearby continuous ensemble of randomly oriented incoherent dipole sources via near‐field interactions. Specifically, a film of colloidal quantum dots is deposited on a plasmonic metasurface consisting of a 1D array of metallic nanoantennas on a metal film. The array is designed to introduce a linear phase profile upon reflection, and a bi‐periodic nanoparticle arrangement is introduced to ensure adequate sampling of the desired phase gradient. Highly directional radiation patterns are correspondingly obtained from the quantum dots at an enhanced emission rate. The underlying radiation mechanism involves the near‐field excitation of surface plasmon polaritons at the metal film, and their selective diffractive scattering by the metasurface into well‐collimated beams along predetermined geometrically tunable directions. These results underscore the distinctive ability of metasurfaces to control radiation properties directly at the source level, which is technologically significant for the continued miniaturization and large‐scale integration of optoelectronic devices.

Tailoring spontaneous infrared emission of HgTe quantum dots with laser-printed plasmonic arrays

Chemically synthesized near-infrared to mid-infrared (IR) colloidal quantum dots (QDs) offer a promising platform for the realization of devices including emitters, detectors, security, and sensor systems. However, at longer wavelengths, the quantum yield of such QDs decreases as the radiative emission rate drops following Fermi’s golden rule, while non-radiative recombination channels compete with light emission. Control over the radiative and non-radiative channels of the IR-emitting QDs is crucially important to improve the performance of IR-range devices. Here, we demonstrate strong enhancement of the spontaneous emission rate of near- to mid-IR HgTe QDs coupled to periodically arranged plasmonic nanoantennas, in the form of nanobumps, produced on the surface of glass-supported Au films via ablation-free direct femtosecond laser printing. The enhancement is achieved by simultaneous radiative coupling of the emission that spectrally matches the first-order lattice resonance of the arrays, as well as more efficient photoluminescence excitation provided by coupling of the pump radiation to the local surface plasmon resonances of the isolated nanoantennas. Moreover, coupling of the HgTe QDs to the lattice plasmons reduces the influence of non-radiative decay losses mediated by the formation of polarons formed between QD surface-trapped carriers and the IR absorption bands of dodecanethiol used as a ligand on the QDs, allowing us to improve the shape of the emission spectrum through a reduction in the spectral dip related to this ligand coupling. Considering the ease of the chemical synthesis and processing of the HgTe QDs combined with the scalability of the direct laser fabrication of nanoantennas with tailored plasmonic responses, our results provide an important step towards the design of IR-range devices for various applications.

Enhanced light-matter interaction in an atomically thin semiconductor coupled with dielectric nano-antennas

Unique structural and optical properties of atomically thin two-dimensional semiconducting transition metal dichalcogenides enable in principle their efficient coupling to photonic cavities having the optical mode volume close to or below the diffraction limit. Recently, it has become possible to make all-dielectric nano-cavities with reduced mode volumes and negligible non-radiative losses. Here, we realise low-loss high-refractive-index dielectric gallium phosphide (GaP) nano-antennas with small mode volumes coupled to atomic mono- and bilayers of WSe{}_{2}. We observe a photoluminescence enhancement exceeding 10{}^{4} compared with WSe{}_{2} placed on planar GaP, and trace its origin to a combination of enhancement of the spontaneous emission rate, favourable modification of the photoluminescence directionality and enhanced optical excitation efficiency. A further effect of the coupling is observed in the photoluminescence polarisation dependence and in the Raman scattering signal enhancement exceeding 10{}^{3}. Our findings reveal dielectric nano-antennas as a promising platform for engineering light-matter coupling in two-dimensional semiconductors.

Enhancement of light emission in Bragg monolayer-thick quantum well structures

Control over spontaneous emission rate is important for improving efficiency in different semiconductor applications including lasers, LEDs and photovoltaics. Usually, an emitter should be placed inside the cavity to increase the spontaneous emission rate, although it is technologically challenging. Here we experimentally demonstrate a phenomenon of super-radiance observed in a cavity-less periodic Bragg structure based on InAs monolayer-thick multiple quantum wells (MQW). The collective super-radiant mode shows enhanced emission rate for specific angles and frequencies. This behaviour correlates with the calculations demonstrating individual spots of the enhanced Purcell coefficient near the Bragg condition curve. This study provides a perspective for realization of surface emitting cavity-less lasers with distributed feedback.

Enhancement of the spontaneous emission rate of Rhodamine 6G molecules coupled into transverse Anderson localized modes in a wedge-type optical waveguide.

In this paper, the dynamics of the spontaneous emission rate of Rhodamine 6G dye molecules, coupled into disorder-induced optical cavities in a scattering medium, is investigated by a time-resolved spectroscopic technique. The system is a wedge-type wave-guiding system formed by a polymer with randomly positioned air inclusions. The scattering of light in the medium induces transverse Anderson localization, which gives rise to quasi-optical modes or Anderson-localized cavities. The presence of these modes strongly enhances the decay emission of the emitters. The waveguide is fabricated by a conventional fiber drawing technique inside a fused silica micro-rod. Localized optical modes are observed to appear in the form of sharp spectral resonance peaks at various frequencies throughout the photoluminescence spectrum of the dye molecules. The spontaneous emission rate of the molecules on resonance with the localized modes is measured to enhance by a factor of up to 6.8, which elucidates that the transverse Anderson localization enables an efficient way to alter the spontaneous emission rate of quantum emitters in an optically asymmetric simple wedge-type photonic waveguide, offering a moderate alternative to highly engineered sophisticated light-wave devices.

Enhancement of Single-Photon Emission Rate from InGaAs/GaAs Quantum-Dot/Nanowire Heterostructure by Wire-Groove Nanocavity.

Spontaneous emission of luminescent material is strongly dependent on the surrounding electromagnetic environment. To enhance the emission rate of a single-photon emitter, we proposed a wire-groove resonant nanocavity around the single-photon emitter. An InGaAs quantum dot embedded in a GaAs nanowire was employed as a site-control single-photon emitter. The nanoscale cavity built by a wire-groove perpendicular to the quantum dot with an extremely narrow width of 10 nm exhibited an extremely small volume of 10 × 40 × 259 nm3. Theoretical analysis showed that the emission rate of the quantum dot was dramatically enhanced by 617x due to the Purcell effect induced by the wire-groove cavity. A fast single-photon emitter with a rate of 50.2 GHz can be obtained that speeds up the data rate of the single-photon emitter. This ultrafast single-photon source would be of great significance in quantum information systems and networks.

Suprathermal nuclear effects in the solar core: overall view

The present paper completes a series of works on the influence on solar processes of fast charged particles produced in exoergic reactions in the solar core. The general picture of suprathermal effects triggered by the most energetic of them—MeV protons and α-particles—is composed. All reactions in the pp chain and the CNO cycle induced by these particles are examined. It is shown that some opposite suprathermal (p, α) and (α, p) reactions can be balanced, but their rates can exceed the rates of the respective thermal processes, affecting some points of nuclear fusion in the solar core. In particular, the suprathermal channels of p + 17O α + 14N reactions increase the total energy released in these processes by a factor of 1.64, and enhance the mass fractions of 17O and 18O by ∼1–4 times at radii . The same result is also obtained for the 18F abundance, leading to the proportional enhancement of the 18F neutrino emission rate. At the same time, integral characteristics like the total energy production and neutrino generation in the solar core remain unchanged.

Simulation technique of quantum optical emission process from multiple two-level atoms based on classical numerical method.

In this paper, we report a numerical method for analyzing optical radiation from a two-level atom. The proposed method can consistently consider the optical emission and absorption process of an atom and also the interaction between atoms through their interaction with a radiation field. The numerical model is based on a damping oscillator description of a dipole current, which is a classical model of atomic transition and is implemented with a finite-difference time-domain method. Using the method, we successfully simulate the spontaneous emission phenomena in a vacuum, where the interaction between an atom and a radiated field plays an important role. We also simulate the radiation from an atom embedded in a photonic crystal (PhC) cavity. As a result, an atom-cavity field interaction is sucessfuly incorporated in the simulation, and the enhancement of the optical emission rate of an excited atom is explained. The method considers the effect of the interaction between atoms through the radiated field. We simulate the optical emission process of the multiple atoms and show that an enhancement of the emission rate can occur owing to an atom-atom interaction (superradiance) (R. H. Dicke, Phys. Rev. 93, 99 [1954]). We also show that the emission rate is suppressed by the effect of the destructive dipole-dipole interaction under an out-of-phase excitation condition (subradiance).

Finite-element method for obtaining the regularized photon Green function in lossy material

The photon Green function (GF) is a vital and decisive factor in the field of quantum light-matter interaction. It is divergent with two equal space arguments in lossy structure and should be regularized. We introduce a finite-element method (FEM) for calculating the regularized GF in arbitrary-shaped lossy structure, which is expressed by the averaged radiation electric field over the finite size of a photon emitter. For an emitter located in a homogeneous lossy material, excellent agreement with the analytical results is found for both real and virtual cavity models. For an emitter located in a metal nano-sphere, the regularized scattered GF, which is the difference between the regularized GF and the analytical regularized one in homogeneous space, agrees well with the analytical scattered GF. Applying this method for an emitter located in a metal nano-rod where there is no analytical solution, we find that the scattering contribution to the enhancement of the spontaneous emission rate is nearly unrelated to the cavity radius while the homogeneous part depends heavily. Our results should be significant for novel photon sources within lossy structures.

Enhancement of the Spontaneous Emission Rate of Perovskite Nanowires Coupled into Cylindrical Hollow Nanocavities Formed on the Surface of Polystyrene Microfibers

Fluorescent CsPbBr3 nanowires are uniformly integrated into a porous polystyrene matrix in the form of microfibers to investigate the changes in their spontaneous emission rate. Cylindrical hollow ...

Light from van der Waals quantum tunneling devices

The understanding of and control over light emission from quantum tunneling has challenged researchers for more than four decades due to the intricate interplay of electrical and optical properties in atomic scale volumes. Here we introduce a device architecture that allows for the disentanglement of electronic and photonic pathways—van der Waals quantum tunneling devices. The electronic properties are defined by a stack of two-dimensional atomic crystals whereas the optical properties are controlled via an external photonic architecture. In van der Waals heterostructures made of gold, hexagonal boron nitride and graphene we find that inelastic tunneling results in the emission of photons and surface plasmon polaritons. By coupling these heterostructures to optical nanocube antennas we achieve resonant enhancement of the photon emission rate in narrow frequency bands by four orders of magnitude. Our results lead the way towards a new generation of nanophotonic devices that are driven by quantum tunneling.

Enhanced quantum dots spontaneous emission with metamaterial perfect absorbers

Metamaterial perfect absorbers (PAs) made of a hexagonal array of holes on Ag-SiO2-Ag thin films have been realized and utilized to enhance the spontaneous emission rate and photoluminescence intensity of CdSe/ZnS quantum dots (QDs) spin-coated on the absorber top surface. Perfect absorption of incoming light occurs at the wavelength where the impedance is matched to that of the free space. When QDs strongly excite both the electric and magnetic resonances at this perfect absorption wavelength, a significant Purcell effect on the spontaneous emission process and enhanced radiative outcoupling of photoluminescence intensity are expected. For perfect absorbers with near-unity absorption at the QD emission wavelength of 620 nm, 5-fold Purcell enhancement of the spontaneous emission rate and 3.6-fold enhancement of photoluminescence intensity are demonstrated in the time-resolved photoluminescence experiments, which are in good agreement with three-dimensional finite-difference time-domain simulation. These results will advance the understanding and applications of metamaterial PA-based light harvesting and emitting devices.

Optical studies of InAs/GaAs monolayer Bragg superlattices

Periodic sequences of InAs monolayer in GaAs have been grown by molecular beam epitaxy. The properties of the structure have been modelled by transfer matrix calculation and experimentally studied by time-resolved photoluminescence. The structure obtained provides good localisation of excitons in quantum wells and opens possibilities for various optical effects. Coupling of excitons in quantum wells with electromagnetic field confined by a Bragg arrangement of layers produces a peculiar emission mode – a superradiant mode. Measurements and calculations show that for specific values of frequency of light and angle of emission, enhancement of spontaneous emission rate occurs.

Optically Addressing Single Rare-Earth Ions in a Nanophotonic Cavity.

We demonstrate optical probing of spectrally resolved single Nd^{3+} rare-earth ions in yttrium orthovanadate. The ions are coupled to a photonic crystal resonator and show strong enhancement of the optical emission rate via the Purcell effect, resulting in near radiatively limited single photon emission. The measured high coupling cooperativity between a single photon and the ion allows for the observation of coherent optical Rabi oscillations. This could enable optically controlled spin qubits, quantum logic gates, and spin-photon interfaces for future quantum networks.

Deterministic coupling of site-controlled quantum emitters in monolayer WSe2 to plasmonic nanocavities.

Solid-state single-quantum emitters are crucial resources for on-chip photonic quantum technologies and require efficient cavity-emitter coupling to realize quantum networks beyond the single-node level1,2. Monolayer WSe2, a transition metal dichalcogenide semiconductor, can host randomly located quantum emitters3-6, while nanobubbles7 as well as lithographically defined arrays of pillars in contact with the transition metal dichalcogenide act as spatially controlled stressors8,9. The induced strain can then create excitons at defined locations. This ability to create zero-dimensional (0D) excitons anywhere within a 2D material is promising for the development of scalable quantum technologies, but so far lacks mature cavity integration and suffers from low emitter quantum yields. Here we demonstrate a deterministic approach to achieve Purcell enhancement at lithographically defined locations using the sharp corners of a metal nanocube for both electric field enhancement and to deform a 2D material. This nanoplasmonic platform allows the study of the same quantum emitter before and after coupling. For a 3 × 4 array of quantum emitters we show Purcell factors of up to 551 (average of 181), single-photon emission rates of up to 42 MHz and a narrow exciton linewidth as low as 55 μeV. Furthermore, the use of flux-grown WSe2 increases the 0D exciton lifetimes to up to 14 ns and the cavity-enhanced quantum yields from an initial value of 1% to up to 65% (average 44%).

Atomic Source of Single Photons in the Telecom Band.

Single atoms and atomlike defects in solids are ideal quantum light sources and memories for quantum networks. However, most atomic transitions are in the ultraviolet-visible portion of the electromagnetic spectrum, where propagation losses in optical fibers are prohibitively large. Here, we observe for the first time the emission of single photons from a single Er^{3+} ion in a solid-state host, whose optical transition at 1.5 μm is in the telecom band, allowing for low-loss propagation in optical fiber. This is enabled by integrating Er^{3+} ions with silicon nanophotonic structures, which results in an enhancement of the photon emission rate by a factor of more than 650. Dozens of distinct ions can be addressed in a single device, and the splitting of the lines in a magnetic field confirms that the optical transitions are coupled to the electronic spin of the Er^{3+} ions. These results are a significant step towards long-distance quantum networks and deterministic quantum logic for photons based on a scalable silicon nanophotonics architecture.

Ultrafast Spontaneous Emission from a Slot-Antenna Coupled WSe2 Monolayer

Optical antennas can enhance the spontaneous emission rate from nanoemitters by orders of magnitude, enabling the possibility of an ultrafast, efficient, nanoscale LED. Semiconductors would be the preferred material for such a device to allow for direct high-speed modulation. However, efficient nanoscale devices are challenging to implement because of high surface recombination typical of most III–V materials. Monolayer transition metal dichalcogenides are an attractive alternative to a III–V emitter due to their intrinsically nanoscale dimensions, direct bandgap, and near-ideal surfaces resulting in high intrinsic quantum yield. In this work, we couple a nanostrip (30 nm × 250 nm) monolayer of WSe2 to a cavity-backed optical slot antenna through a self-aligned fabrication process. Photoluminescence, scattering, and lifetime measurements are used to estimate a radiative spontaneous emission rate enhancement of 318× from WSe2 monolayers coupled to on-resonance antennas. Such a huge increase in the spontane...