Large Purcell Factor Research Articles

DNA-mediated assembly of Au bipyramids into anisotropic light emitting kagome superlattices.

Colloidal crystal engineering with DNA allows one to design diverse superlattices with tunable lattice symmetry, composition, and spacing. Most of these structures follow the complementary contact model, maximizing DNA hybridization on building blocks and producing relatively close-packed lattices. Here, low-symmetry kagome superlattices are assembled from DNA-modified gold bipyramids that can engage only in partial DNA surface matching. The bipyramid dimensions and DNA length can be engineered for two different superlattices with rhombohedral unit cells, including one composed of a periodic stacking of kagome lattices. Enabled by the partial facet alignment, the kagome lattices exhibit lattice distortion, bipyramid twisting, and planar chirality. When conjugated with Cy-5 dyes, the kagome lattices serve as cavities with high-density optical states and large Purcell factors along lateral directions, leading to strong dipole radiation along the z axis and facet-dependent light emission. Such complex optical properties make these materials attractive for lasers, displays, and quantum sensing constructs.

Multi-wavelength unidirectional forward scattering properties of the arrow-shaped galliumphosphide nanoantenna.

An arrow-shaped gallium phosphide nanoantenna exhibits both near-field electric field enhancement and far-field unidirectional scattering, and the interference conditions involve electric and magnetic quadrupoles as well as toroidal dipoles. By using long-wavelength approximation and exact multipole decomposition, the interference conditions required for far-field unidirectional transverse light scattering and backward near-zero scattering at multiple wavelengths are determined. The near-field properties are excellent, as exemplified by large Purcell factors of 4.5×109 for electric dipole source excitation, 464.68 for magnetic dipole source excitation, and 700V/m for the field enhancement factor. The degree of enhancement of unidirectional scattering is affected by structural parameters such as the angle and thickness of the nanoantenna. The arrow-shaped nanoantenna is an efficient platform to enhance the electric field and achieve high directionality of light scattering. Moreover, the nanostructure enables flexible manipulation of light waves and materials, giving rise to superior near-field and far-field performances, which are of great importance pertaining to the practicability and application potential of optical antennas in applications such as spectroscopy, sensing, displays, and optoelectronic devices.

Hybrid dielectric slot-plasmonic ring resonator for Purcell enhancement

We present a computational study of Purcell factor enhancement for a novel hybrid-plasmonic ring resonator using a novel implementation of the body-of-revolution (BOR) finite-difference time-domain (FDTD) method. In this hybrid structure, a dielectric slot ring is surrounded by a metallic ring such that a hybrid plasmonic mode is generated within two thin low-index gaps. The surrounding metallic ring decreases the binding loss for small ring radii, leading to high-quality factors and mode-field confinement. The hybrid resonator shows high quality-factor values above 103 and small mode volumes down to simultaneously, thus providing large Purcell factors (F p > 104). The distributed strong confinement within two gaps renders the proposed resonator useful for multi-emitter applications.

Indistinguishable telecom band photons from a single Er ion in the solid state.

Atomic defects in the solid state are a key component of quantum repeater networks for long-distance quantum communication1. Recently, there has been significant interest in rare earth ions2-4, in particular Er3+ for its telecom band optical transition5-7 that allows long-distance transmission in optical fibres. However, the development of repeater nodes based on rare earth ions has been hampered by optical spectral diffusion, precluding indistinguishable single-photon generation. Here, we implant Er3+ into CaWO4, a material that combines a non-polar site symmetry, low decoherence from nuclear spins8 and is free of background rare earth ions, to realize significantly reduced optical spectral diffusion. For shallow implanted ions coupled to nanophotonic cavities with large Purcell factor, we observe single-scan optical linewidths of 150 kHz and long-term spectral diffusion of 63 kHz, both close to the Purcell-enhanced radiative linewidth of 21 kHz. This enables the observation of Hong-Ou-Mandel interference9 between successively emitted photons with a visibility of V = 80(4)%, measured after a 36 km delay line. We also observe spin relaxation times T1,s = 3.7 s and T2,s > 200 μs, with the latter limited by paramagnetic impurities in the crystal instead of nuclear spins. This represents a notable step towards the construction of telecom band quantum repeater networks with single Er3+ ions.

Hybrid Photonic-Plasmonic Cavity Design for Very Large Purcell Factors at Telecommunication Wavelengths

Hybrid photonic-plasmonic cavities based on nanoparticle-on-a-mirror structures simultaneously provide ultralow mode volume and high $Q$-factor, and so a very large Purcell factor, which is a key measure of light-matter interaction. Operation of such cavities has been constrained to wavelengths below 1 \ensuremath{\mu}m, with the technologically relevant telecom regime remaining elusive. This study describes a hybrid cavity operating at telecom wavelengths. The proposed design leads to extremely large Purcell factors (~10${}^{7}$--10${}^{8}$), and could impact many different applications, such as molecular optomechanics, bio- and chemosensing, efficient quantum emitters, and enhanced Raman spectroscopy.

Topological insulator nanoparticles for strong light-matter interaction in the terahertz regime.

We study the spontaneous emission (SPEM) for a quantum emitter (QUEM) near a topological insulator Bi2Se3 nanosphere. We calculate numerically the QUEM Purcell factor near nanospheres of radii between 40 nm and 100 nm, with and without taking into account the topologically protected delocalized states at the surface of the nanosphere. We find exceptionally large Purcell factors up to 1010 at distances between the QUEM and the nanosphere as large as half its radius in the terahertz regime. By computing the SPEM dynamics for a QUEM with transition frequencies in the terahertz and free-space decay rates in the nanosecond to millisecond range, we observe intense reversible dynamics, as well as population trapping effects. This work demonstrates that a Bi2Se3 nanosphere provides the conditions for strong light-matter interaction at the nanoscale in the terahertz regime.

Near-zero-index-featured multi-band highly directional radiator with large Purcell factors

Near-zero-index medium could be used to produce perfect planar wave beams, allowing for the design of compact antennas, but implementation is difficult due to the bandwidth and loss limitations. This work proposes a new method for achieving highly directional radiation by introducing a near-zero-index-featured resonator based on optical conformal mapping. The conceptual device performs the same functions as resonators filled with near-zero-index media but can be realized using dielectrics with refractive index n ≥ 1. Multi-band highly directional radiation with large Purcell factor is numerically demonstrated by the proposed high-Q resonator, which may pave the way for efficient production of high gain directive antennas in radar systems.

Purcell factors and Förster-resonance energy transfer in proximity to helical structures

Both spontaneous emission and resonant energy transfer can be enhanced significantly when the emitter is placed in the vicinity of metallic or crystal structures. This enhancement can be described using the electromagnetic Green tensor and is determined by the dominant surface modes of the structure. Here we use the eigenpermittivity formalism to derive the spontaneous emission and FRET rates in the quasistatic regime in a two-constituent medium with an anisotropic inclusion. We then apply our results to a helical structure supporting synchronous vibrations and evaluate the contribution of these modes, which are associated with a strong and delocalized response. We show that this contribution can result in large Purcell factors and long-range FRET, which oscillates with the helix pitch. These findings may have implications in understanding and controlling the interactions of molecules close to helical structures such as the microtubules.

Silicon cuboid nanoantenna with simultaneous large Purcell factor for electric dipole, magnetic dipole and electric quadrupole emission

The Purcell effect is commonly used to increase the spontaneous emission rate by modifying the local environment of a light emitter. Here, we propose a silicon dielectric cuboid nanoantenna for simultaneously enhancing electric dipole (ED), magnetic dipole (MD) and electric quadrupole (EQ) emission. We study the scattering cross section, polarization charge distribution, and electromagnetic field distribution for electromagnetic plane wave illuminating the silicon dielectric cuboid nanoantenna, from which we have identified simultaneous existence of ED, MD and EQ resonance modes in this nanoantenna. We have calculated the Purcell factor of ED, MD and EQ emitters with different moment orientations as a function of radiation wavelength by placing these point radiation source within the nanoantenna, respectively. We find that the resonances wavelengths of the Purcell factor spectrum are matching with the resonance modes in the nanoantenna. Moreover, the maximum Purcell factor of these ED, MD and EQ emitters is 18, 150 and 118 respectively, occurring at the resonance wavelength of 475, 750, and 562 nm, respectively, all within the visible range. The polarization charge distribution features allow us to clarify the excitation and radiation of these resonance modes as the physical origin of large Purcell factor simultaneously occurring in this silicon cuboid nanoantenna. Our theoretical results might help to deeply explore and design the dielectric nanoantenna as an ideal candidate to enhance ED, MD and EQ emission simultaneously with very small loss in the visible range, which is superior than the more popular scheme of plasmonic nanoantenna.

Ultra-compact titanium dioxide micro-ring resonators with sub-10-μm radius for on-chip photonics

Microring resonators (MRRs) with ultracompact footprints are preferred for enhancing the light-matter interactions to benefit various applications. Here, ultracompact titanium dioxide ( TiO 2 ) MRRs with sub-10-μm radii are experimentally demonstrated. Thanks to the large refractive index of TiO 2 , the quality factors up to ∼ 7.9 × 10 4 and ∼ 4.4 × 10 4 are achieved for TiO 2 MRRs with radii of 10 μm and 6 μm, respectively, which result in large nonlinear power enhancement factors ( > 113 ) and large Purcell factors ( > 56 ). The four-wave mixing (FWM) measurements indicate that, compared to the large MRR, the FWM conversion efficiency of the ultracompact TiO 2 MRRs can be greatly improved (e.g., − 25 dB versus − 31 dB ), a harbinger of significant superiorities. Demonstrations in this work provide more arguments for the TiO 2 waveguides as a promising platform for various on-chip photonic devices.

Topology-Enhanced Nonreciprocal Scattering and Photon Absorption in a Waveguide

Topological matter and topological optics have been studied in many systems, with promising applications in materials science and photonics technology. These advances motivate the study of the interaction between topological matter and light, as well as topological protection in light-matter interactions. In this work, we study a waveguide-interfaced topological atom array. The light-matter interaction is nontrivially modified by topology, yielding novel optical phenomena. We find topology-enhanced photon absorption from the waveguide for large Purcell factor, i.e., $\Gamma/\Gamma_0\gg 1$, where $\Gamma$ and $\Gamma_0$ are the atomic decays to waveguide and environment, respectively. To understand this unconventional photon absorption, we propose a multi-channel scattering approach and study the interaction spectra for edge- and bulk-state channels. We find that, by breaking inversion and time-reversal symmetries, optical anisotropy is enabled for reflection process, but the transmission is isotropic. Through a perturbation analysis of the edge-state channel, we show that the anisotropy in the reflection process originates from the waveguide-mediated non-Hermitian interaction. However, the inversion symmetry in the non-Hermitian interaction makes the transmission isotropic. At a topology-protected atomic spacing, the subradiant edge state exhibits huge anisotropy. Due to the interplay between edge- and bulk-state channels, a large topological bandgap enhances nonreciprocal reflection of photons in the waveguide for weakly broken time-reversal symmetry, i.e., $\Gamma_0/\Gamma\ll 1$, producing complete photon absorption. We show that our proposal can be implemented in superconducting quantum circuits. The topology-enhanced photon absorption is useful for quantum detection. This work shows the potential to manipulate light with topological quantum matter.

Time-frequency encoded single-photon generation and broadband single-photon storage with a tunable subradiant state

An atomic system that can be addressed via a single optical mode, hereafter called a one-dimensional atom, is central for many applications in optical quantum technologies. A cavity with a large Purcell factor is required to collect the emission efficiently, but a small Purcell factor is required for long-time memory storage. Here, we introduce an effective and versatile one-dimensional atom consisting of two interacting quantum emitters efficiently coupled to a cavity mode with a large Purcell factor. The dipole–dipole interaction gives rise to a subradiant state with a tunable bandwidth. We demonstrate generation of time-shaped single photons and implementation of quantum memory. We discuss experimental challenges and practical implementation using different systems.

Effects of gap thickness and emitter location on the photoluminescence enhancement of monolayer MoS2 in a plasmonic nanoparticle-film coupled system

Abstract Plasmonic nanocavities comprised of metal film-coupled nanoparticles have emerged as a versatile nanophotonic platform benefiting from their ultrasmall mode volume and large Purcell factors. In the weak-coupling regime, the particle-film gap thickness affects the photoluminescence (PL) of quantum emitters sandwiched therein. Here, we investigated the Purcell effect-enhanced PL of monolayer MoS2 inserted in the gap of a gold nanoparticle (AuNP)–alumina (Al2O3)–gold film (Au Film) structure. Under confocal illumination by a 532 nm CW laser, we observed a 7-fold PL peak intensity enhancement for the cavity-sandwiched MoS2 at an optimal Al2O3 thickness of 5 nm, corresponding to a local PL enhancement of ∼350 by normalizing the actual illumination area to the cavity’s effective near-field enhancement area. Full-wave simulations reveal a counterintuitive fact that radiation enhancement comes from the non-central area of the cavity rather than the cavity center. By scanning an electric dipole across the nanocavity, we obtained an average radiation enhancement factor of about 65 for an Al2O3 spacer thickness of 4 nm, agreeing well with the experimental thickness and indicating further PL enhancement optimization. Our results indicate the importance of configuration optimization, emitter location and excitation condition when using such plasmonic nanocavities to modulate the radiation properties of quantum emitters.

Metal-dielectric nanoantenna for radiation control of a single-photon emitter

The control of fluorescent properties of single-photon sources in solid-state host systems via optically resonant nanostructures is a key issue in quantum nanophotonics. Here we propose a design of a resonant metal-dielectric nanoantenna for the Purcell factor and radiation pattern control of a quantum emitter placed in the gap between metal and dielectric components of the nanostructure. We demonstrate that large Purcell factor, considerable field enhancement in the gap as well as high directivity can be achieved. The developed nanosystem can be utilized for different solid-state host systems from nanocrystals to 2D materials.

Theory and Limits of On-Demand Single-Photon Sources Using Plasmonic Resonators: A Quantized Quasinormal Mode Approach

Quantum emitters coupled to plasmonic resonators are known to allow enhanced broadband Purcell factors, and such systems have been recently suggested as possible candidates for on-demand single photon sources, with fast operation speeds. However, a true single photon source has strict requirements of high efficiency (brightness) and quantum indistinguishability of the emitted photons, which can be quantified through two-photon interference experiments. To help address this problem, we employ and extend a recently developed quantized quasinormal mode approach, which rigorously quantizes arbitrarily lossy open system modes, to compute the key parameters that accurately quantify the figures of merit for plasmon-based single photon sources. We also present a quantized input-output theory to quantify the radiative and nonradiative quantum efficiencies. We exemplify the theory using a nanoplasmonic dimer resonator made up of two gold nanorods, which yields large Purcell factors and good radiative output beta factors. Considering an optically pulsed excitation scheme, we explore the key roles of pulse duration and pure dephasing on the single photon properties, and show that ultrashort pulses (sub-ps) are generally required for such structures, even for low temperature operation. We also quantify the role of the nonradiative beta factor both for single photon and two-photon emission processes. Our general approach can be applied to a wide variety of plasmon systems, including metal-dielectrics, and cavity-waveguide systems, without recourse to phenomenological quantization schemes.

Study of cavity-enhanced dipole emission on a hyperbolic metamaterial slab

We theoretically study strong coupling of a dipole emitter positioned close to a hyperbolic metamaterial (HMM) slab. Enhanced dipole emission with a large Purcell factor originated from the superposition of p-wave resonant coupling and critical coupling to the high-k waveguide modes in a HMM slab is addressed, and the dependence of the slab thickness and the fill ratio of metallic nanorods in HMM on the emission strength is explicitly summarized. Via optimizing the mode coupling condition, we point out a general design rule for the HMM structure to yield a large Purcell factor. Furthermore, by incorporating a Si bullseye grating on the HMM slab, 18-fold far-field radiation enhancement owing to extraction of the mainly coupled resonant mode in HMM is presented.

Highly Directive Hybrid Metal-Dielectric Yagi-Uda Nanoantennas.

A hybrid metal-dielectric nanoantenna promises to harness the large Purcell factor of metallic nanostructures while taking advantage of the high scattering directivity and low dissipative losses of dielectric nanostructures. Here, we investigate a compact hybrid metal-dielectric nanoantenna that is inspired by the Yagi-Uda design. It comprises a metallic gold bowtie nanoantenna feed element and three silicon nanorod directors, exhibiting high unidirectional in-plane directivity and potential beam redirection capability in the visible spectral range. The entire device has a footprint of only 0.38 λ2, and its forward directivity is robust against fabrication imperfections. We use the photoluminescence from the gold bowtie nanoantenna itself as an elegant emitter to characterize the directivity of the device and experimentally demonstrate a directivity of ∼49.2. In addition, we demonstrate beam redirection with our device, achieving a 5° rotation of the main emission lobe with a feed element displacement of only 16 nm. These results are promising for various applications, including on-chip wireless communications, quantum computing, display technologies, and nanoscale alignment.

Hybridized Plasmonic Gap Mode of Gold Nanorod on Mirror Nanoantenna for Spectrally Tailored Fluorescence Enhancement

Plasmonic nanoparticle on mirror antennas with sub-10 nm gaps have shown the great potential in nanophotonic applications because they offer tightly confined electric field in the gap and resultant large Purcell factors. However, in a nanosphere on mirror (NSoM) structure being studied experimentally, the degree of freedom of the antennas in terms of spectral and polarization control is limited. In this work, we report spectral shaping and polarization control of Purcell-enhanced fluorescence by the gap plasmon modes of an anisotropic gold (Au) nanorod on a mirror (NRoM) antenna. Systematic numerical calculations demonstrate the richer resonance behaviors of a NRoM antenna than a NSoM antenna due to the hybridization of the bright and dark modes. We fabricate a NRoM antenna by placing a Au NR on an ultraflat Au film via a mono-, double-, or quadruple-layers of light emitting quantum dots (QDs) (3 nm in diameter). The scattering spectra of single NRoM antennas coincide very well with those of the numerical...

Titania‐Based Spherical Mie Resonators Elaborated by High‐Throughput Aerosol Spray: Single Object Investigation

AbstractIn the framework of photonics with all‐dielectric nanoantennas, sub‐micrometric spheres can be exploited for a plethora of applications including vanishing back‐scattering, enhanced directivity of a light emitter, beam steering, and large Purcell factors. Here, the potential of a high‐throughput fabrication method based on aerosol‐spray is shown to form quasi‐perfect sub‐micrometric spheres of polycrystalline TiO2. Spectroscopic investigation of light scattering from individual particles reveals sharp resonances in agreement with Mie theory, neat structural colors, and a high directivity. Owing to the high permittivity and lossless material in use, this method opens the way toward the implementation of isotropic meta‐materials and forward‐directional sources with magnetic responses at visible and near‐UV frequencies, not accessible with conventional Si‐ and Ge‐based Mie resonators.

Vertical pillar nanoantenna for emission enhancement and redirection

Designing efficient metallic nanostructures can help in realizing bright single photon emission in the visible and near-infrared ranges. We propose a novel nanostructure design that combines the benefits of plasmonic hot spot generation in the near-field and the concept of antennas developed in the radio-frequency range. The antenna is formed by a vertical stack of metallic and dielectric nanocylinders. When used for controlling the far-field emission of a localized source, its key features are moderate losses in the metal, relatively large Purcell factors, as well as a low sensibility to the lateral position of the emitter. A redirection process necessary for these vertical structures is proposed, based on the versatility of the vertical geometry, and allows an efficient redirection of the emitted light even for antennas on dielectric substrates.