Micropillar Cavities Research Articles

Polariton surface solitons under a resonant pump.

We address the formation of stable dissipative surface solitons in the exciton-polariton condensate in a one-dimensional array of microcavity pillars under the action of a localized resonant pump acting in the edge resonator. We show that the localization degree and peak amplitudes of surface solitons can be effectively controlled by the pump frequency and that the allowed energy gap of the periodic structure determines the energy range, where surface solitons can form. One observes bistability at sufficiently large pump amplitudes and a nonlinearity-induced shift of the position of the resonance peak from the allowed energy band of the periodic array into its forbidden energy gap. The growth of the spatial period of the array reduces coupling between pillars and currents from a surface pillar into bulk pillars which leads to the increase of the surface soliton amplitude. Strong expansion into the depth of the array occurs for pump frequencies corresponding to the middle of the allowed energy band. Surface solitons can be excited from the broadband Gaussian noise. Above certain threshold noise levels, solitons from a stable upper branch of the bistability curve are excited while, below threshold, solitons from the lower branch form.

Resource-efficient analyzer of Bell and Greenberger-Horne-Zeilinger states of multiphoton systems

We propose a resource-efficient error-rejecting entangled-state analyzer for polarization-encoded multiphoton systems. Our analyzer is based on two single-photon quantum-nondemolition detectors, where each of them is implemented with a four-level emitter (e.g., a quantum dot) coupled to a one-dimensional system (such as a micropillar cavity or a photonic nanocrystal waveguide). The analyzer works in a passive way and can completely distinguish $2^n$ Greenberger-Horne-Zeilinger~(GHZ) states of $n$ photons without using any active operation or fast switching. The efficiency and fidelity of the GHZ-state analysis can, in principle, be close to unity, when an ideal single-photon scattering condition is fulfilled. For a nonideal scattering, which typically reduces the fidelity of a GHZ-state analysis, we introduce a passively error-rejecting circuit to enable a near-perfect fidelity at the expense of a slight decrease of its efficiency. Furthermore, the protocol can be directly used to perform a two-photon Bell-state analysis. This passive, resource-efficient, and error-rejecting protocol can, therefore, be useful for practical quantum networks.

Finite‐Dimensional Bistable Topological Insulators: From Small to Large

AbstractPhotonic topological insulators supporting unidirectional topologically protected edge states represent an attractive platform for the realization of disorder‐ and backscattering‐immune transport of edge excitations in both linear and nonlinear regimes. While the properties of the edge states at unclosed interfaces of two bulk media with different topologies are known, the existence of edge states in practical finite‐dimensional topological insulators fully immersed in a nontopological environment remains largely unexplored. In this work, using realistic polariton topological insulators built from small‐size honeycomb arrays of microcavity pillars as an example, it is shown how topological properties of the system build up upon gradual increase of its dimensionality. To account for the dissipative nature of the polariton condensate forming in the array of microcavity pillars, the impact of losses and resonant pump leading to rich bistability effects in this system is considered. The mechanism is described in accordance with which trivial‐phase pump “selects” and excites specific nonlinear topological edge states circulating along the periphery of the structure in the azimuthal direction, dictated by the direction of the external applied magnetic field. The possibility of utilization of vortex pump with different topological charges for selective excitation of different edge currents is also shown.

Pseudodrag of a polariton superfluid

The drag of half-light half-mater quasiparticles, exciton-polaritons, by an electric current is a peculiar mechanism of light-matter interaction in solids. While an ideal superfluid is protected from being dragged by its zero viscosity, here we argue that the state of the superfluid polariton condensate formed by a non-resonant optical pumping can be controlled by the electric current. The proposed mechanism is based on the stimulated relaxation of moving uncondensed excitons dragged by the electric current. The stimulated relaxation process favors the formation of a moving condensate in a quantum state that is characterised by the lowest condensation threshold. We also show that the electron-mediated inelastic scattering of the reservoir excitons to the condensate leads to the transfer of a non-zero mean momentum to the electron gas thus contributing to the electric current. We predict the generation of circular electric currents in a micropillar cavity in the presence of a nonresonant laser pumping at normal incidence.

Brillouin scattering in hybrid optophononic Bragg micropillar resonators at 300 GHz

We introduce a monolithic Brillouin generator based on a semiconductor micropillar cavity embedding a high frequency nanoacoustic resonator operating in the hundreds of GHz range. The concept of two nested resonators allows an independent design of the ultrahigh frequency Brillouin spectrum and of the optical device. We develop an optical free-space technique to characterize spontaneous Brillouin scattering in this monolithic device and propose a measurement protocol that maximizes the Brillouin generation efficiency in the presence of optically induced thermal effects. The compact and versatile Brillouin generator studied here could be readily integrated into fibered and on-chip architectures.

Strain-Tunable Single-Photon Source Based on a Quantum Dot–Micropillar System

Scalable quantum photonic architectures demand highly efficient, high-purity single-photon sources, which can be frequency matched via external tuning. We demonstrate a single-photon source based on an InAs quantum dot embedded in a micropillar resonator, which is frequency tunable via externally-applied stress. Our platform combines the advantages of a Bragg micropillar cavity and the piezo-strain-tuning technique enabling single photon spontaneous emission enhancement via the Purcell effect and quantum dot (QD) with tunable wavelength. Our optomechanical platform has been implemented by integration of semiconductor-based QD-micropillars on a piezoelectric substrate. The fabricated device exhibits spontaneous emission enhancement with a Purcell factor of 4.4$\pm$0.7 and allows for a pure triggered single-photon generation with $g^{(2)}(0)$ < 0.07 under resonant excitation. A quantum dot emission energy tuning range of 0.75 meV for 27 kV/cm applied to the piezo substrate has been achieved. Our results pave the way towards the scalable implementation of single-photon quantum photonic technologies using optoelectronic devices.

Interface states in polariton topological insulators

We address linear and nonlinear topological interface states in polariton condensates excited at the interface of the honeycomb and Lieb arrays of microcavity pillars in the presence of spin-orbit coupling and Zeeman splitting in the external magnetic field. Such interface states appear only in total energy gaps of the composite structure when parameters of the honeycomb and Lieb arrays are selected such that some topological gaps in the spectrum of one of the arrays overlap with topological or nontopological gaps in the spectrum of the other array. This is in contrast to conventional edge states at the interface of periodic topological and uniform trivial insulators, whose behavior is determined exclusively by the spectrum of the topological medium. The number of emerging interface states is determined by the difference of the Chern numbers of the overlapping gaps. Illustrative examples with one or two coexisting unidirectional interface states are provided. The representative feature of the system is the possibility of wide tuning of the concentration of power of the interface states between two limiting cases when practically all power is concentrated either in the Lieb or the honeycomb array. Localization of the interface states and their penetration depth into arrays drastically vary with Bloch momentum or upon modification of the amplitude of the interface state in the nonlinear regime. We illustrate topological protection of the interface states manifested in the absence of backscattering on interface defects, and study their modulation instability in the nonlinear regime. The latter leads to formation of quasisolitons whose penetration into different arrays also depends on Bloch momentum. In addition, we discuss the impact of losses and coherent pump leading to bistability of the interface states.

Quantum Frequency Conversion of a Quantum Dot Single-Photon Source on a Nanophotonic Chip.

Single self-assembled InAs/GaAs quantum dots are promising bright sources of indistinguishable photons for quantum information science. However, their distribution in emission wavelength, due to inhomogeneous broadening inherent to their growth, has limited the ability to create multiple identical sources. Quantum frequency conversion can overcome this issue, particularly if implemented using scalable chip-integrated technologies. Here, we report the first demonstration of quantum frequency conversion of a quantum dot single-photon source on a silicon nanophotonic chip. Single photons from a quantum dot in a micropillar cavity are shifted in wavelength with an on-chip conversion efficiency ≈ 12 %, limited by the linewidth of the quantum dot photons. The intensity autocorrelation function for the frequency-converted light is antibunched with , compared to the before-conversion value . We demonstrate the suitability of our frequency conversion interface as a resource for quantum dot sources by characterizing its effectiveness across a wide span of input wavelengths (840 nm to 980 nm), and its ability to achieve tunable wavelength shifts difficult to obtain by other approaches.

Ultrafast pulse phase shifts in a charged-quantum-dot–micropillar system

We employ a quantum master equations approach based on a vectorial Maxwell-pseudospin model to compute the quantum evolution of the spin populations and coherences in the fundamental singlet trion transition of a negatively charged quantum dot embedded in a micropillar cavity. Excitation of the system is achieved through an ultrashort, either circularly or linearly polarised resonant pulse. By implementing a realistic micropillar cavity geometry, we numerically demonstrate a giant optical phase shift ($\sim \pm \pi/2$) of a resonant circularly polarised pulse in the weak-coupling regime. The phase shift that we predict considerably exceeds the experimentally observed Kerr rotation angle $(\sim{6 ^{\circ}})$ under a continuous-wave, linearly polarised excitation. By contrast, we show that a linearly polarised pulse is rotated to a much lesser extent of a few degrees. Depending on the initial boundary conditions, this is due to either retardation or advancement in the amplitude build-up in time of the orthogonal electric field component. Unlike previous published work, the dominant spin relaxation and decoherence processes are fully accounted for in the system dynamics. Our dynamical model can be used for optimisation of the optical polarisation rotation angle for realisation of spin-photon entanglement and ultrafast polarisation switching on a chip.

Study of non-isothermal liquid evaporation in synthetic micro-pore structures with hybrid lattice Boltzmann model

Non-isothermal liquid evaporation in micro-pore structures is studied experimentally and numerically using the lattice Boltzmann method. A hybrid thermal entropic multiple-relaxation-time multiphase lattice Boltzmann model (T-EMRT-MP LBM) is implemented and validated with experiments of droplet evaporation on a heated hydrophobic substrate. Then liquid evaporation is investigated in two specific pore structures, i.e. spiral-shaped and gradient-shaped micro-pillar cavities, referred to as SMS and GMS, respectively. In SMS, the liquid receding front follows the spiral pattern; while in GMS, the receding front moves layer by layer from the pillar rows with large pitch to the rows with small one. Both simulations agree well with experiments. Moreover, evaporative cooling effects in liquid and vapour are observed and explained with simulation results. Quantitatively, in both SMS and GMS, the change of liquid mass with time coincides with experimental measurements. The evaporation rate generally decreases slightly with time mainly because of the reduction of liquid–vapour interface. Isolated liquid films in SMS increase the evaporation rate temporarily resulting in local peaks in evaporation rate. Reynolds and capillary numbers show that the liquid internal flow is laminar and that the capillary forces are dominant resulting in menisci pinned to the pillars. Similar Péclet number is found in simulations and experiments, indicating a diffusive type of heat, liquid and vapour transport. Our numerical and experimental studies indicate a method for controlling liquid evaporation paths in micro-pore structures and maintaining high evaporation rate by specific geometry designs.

High spectral resolution of GaAs/AlAs phononic cavities by subharmonic resonant pump-probe excitation

We present here precise measurement of the resonance frequency, lifetime and shape of confined acoustic modes in the tens of GHz regime in GaAs/AlAs superlattice planar and micropillar cavities at low temperature ($\sim 20\,\textrm{K}$). The subharmonic resonant pump-probe technique, where the repetition rate of the pump laser is tuned to a subharmonic of the cavity resonance to maximize the amplitude of the acoustic resonance, in combination with a Sagnac interferometer technique for high sensitivity ($\sim 10 \,\textrm{fm}$) to the surface displacement, has been used. The cavity fundamental mode at $\sim 20\,\textrm{GHz}$ and the higher order cavity harmonics up to $\sim 180\,\textrm{GHz}$ have been clearly resolved. Mechanical Q-values up to $2.7 \times 10^4$ have been measured in a planar superlattice, and direct spatial mapping of confined acoustic modes in a superlattice cavity micropillar has been demonstrated. The Q-frequency product obtained is $ \sim 5 \times 10^{14}$ demonstrating the suitability of these superlattice cavities for optomechanical applications.

Error-detected single-photon quantum routing using a quantum dot and a double-sided microcavity system**Project supported by the Scientific Research Foundation of Shanxi Institute of Technology (Grant No. 201706001), the Fund for Shanxi “1331 Project” Key Subjects Construction, the China Postdoctoral Science Foundation (Grant No. 2017M612411), the Education Department Foundation of Henan Province, China (Grant No. 18A140009), and the National Natural Science

Based on a hybrid system consisting of a quantum dot coupled with a double-sided micropillar cavity, we investigate the implementation of an error-detected photonic quantum routing controlled by the other photon. The computational errors from unexpected experimental imperfections are heralded by single photon detections, resulting in a unit fidelity for the present scheme, so that this scheme is intrinsically robust. We discuss the performance of the scheme with currently achievable experimental parameters. Our results show that the present scheme is efficient. Furthermore, our scheme could provide a promising building block for quantum networks and distributed quantum information processing in the future.

Simulation of two-boson bound states using arrays of driven-dissipative coupled linear optical resonators

We present a strategy based on two-dimensional arrays of coupled linear optical resonators to investigate the two-body physics of interacting bosons in one-dimensional lattices. In particular, we want to address the bound pairs in topologically non-trivial Su-Schrieffer-Heeger arrays. Taking advantage of the driven-dissipative nature of the resonators, we propose spectroscopic protocols to detect and tomographically characterize bulk doublon bands and doublon edge states from the spatially-resolved transmission spectra, and to highlight Feshbach resonance effects in two-body collision processes. We discuss the experimental feasibility using state-of-the-art devices, with a specific eye on arrays of semiconductor micropillar cavities.

Scaling rules in optomechanical semiconductor micropillars

Semiconductor pillar microcavities have recently emerged as a promising optomechanical platform in the unprecedented 20-GHz frequency range. Currently established models for the mechanical behavior of micropillars, however, rely on complete numerical simulations or semianalytical approaches, which makes their application to experiments notoriously difficult. Here we overcome this challenge with an effective model by reducing the full, hybridized mechanical mode picture of a micropillar to an approach that captures the observed global trends. We show experimentally the validity of this approach by studying the lateral size dependence of the frequency, amplitude, and lifetime of the mechanical modes of square-section pillar microcavities, using room-temperature pump-probe microscopy. General scaling rules for these quantities are found and explained through simple phenomenological models of the physical phenomena involved. We show that the energy shift $\mathrm{\ensuremath{\Delta}}{\ensuremath{\omega}}_{m}$ of the modes due to confinement is dependent on the inverse of their frequency ${\ensuremath{\omega}}_{0}$ and lateral size $L$ ($\mathrm{\ensuremath{\Delta}}{\ensuremath{\omega}}_{m}\ensuremath{\propto}1/{\ensuremath{\omega}}_{0}{L}^{2}$) and that the mode lifetime $\ensuremath{\tau}$ is linear with pillar size and inversely proportional to their frequency ($\ensuremath{\tau}\ensuremath{\propto}L/{\ensuremath{\omega}}_{0}$). The mode amplitude is in turn inversely proportional to the lateral size of the considered resonators. This is related to the dependence of the optomechanical coupling rate (${g}_{0}\ensuremath{\propto}1/L$) with the spatial extent of the confined electromagnetic and mechanical fields. Using a numerical model based on the finite-element method, we determine the magnitude and size dependence of ${g}_{0}$ and, by combining the results with the experimental data, we discuss the attainable single-photon cooperativity in these systems. The effective models proposed and the scaling rules found constitute an important tool in micropillar optomechanics and in the future development of more complex micropillar based devices.

Inhibition of tunneling and edge state control in polariton topological insulators

We address the inhibition of tunneling in polariton condensates confined in a potential landscape created by a honeycomb array of microcavity pillars in the presence of spin-orbit coupling and Zeeman splitting in the external magnetic field. The coupling rate between the microcavity pillars can be strongly impacted even by weak out-of-phase temporal modulations of the depths of the corresponding potential wells. When such a modulation is implemented in truncated honeycomb arrays that realize a polariton topological insulator, which supports unidirectional edge states in the presence of spin-orbit coupling and Zeeman splitting, it allows controlling the velocity of the states. The origin of the phenomenon is the dynamical modulation with a proper frequency, which notably changes the dispersion of the system and the group velocity of edge states. We show that such a control is possible for modulation frequencies close to resonances for the inhibition of tunneling in a two-well configuration. Edge states considerably slow down, and even stop completely, when the modulation frequency approaches a resonant value, while above such a frequency, splitting of the edge states into wavepackets moving with different velocities occurs.

Fabrication of dense diameter-tuned quantum dot micropillar arrays for applications in photonic information processing

We report on the realization of a dense, large-scale array of 900 quantum dot micropillar cavities with high spectral homogeneity. We target applications in photonic information processing such as optical reservoir computing which can be implemented in large arrays of optically coupled microlasers. To achieve the required spectral homogeneity for the underlying optical injection locking, we calculate and set the diameter of each individual micropillar within the array during the fabrication process by taking the diameter-dependent emission wavelength of the microcavities into account. Using this kind of diameter adjustment, we improve the overall wavelength homogeneity in a 30 × 30 micropillar array by 64% and reduce the standard deviation of the resonance energy distribution by 26% from 352 μeV in the planar unprocessed sample to 262 μeV in the fabricated array. In addition, we present a detailed analysis of the device quality and the diameter control of the micropillar’s emission wavelength, which includes important information for the effective application of the developed fabrication method for the realization of highly homogeneous micropillar arrays in the future.

Generating orthogonally polarized dual frequency combs with slow megahertz repetition rates by a low-nanowatt-level pump

Dual frequency comb generation has been the focus of many recent research efforts owing to its viability in a myriad of applications, ranging from precision measurement to high-speed optical communications. Here, with the state of the art of a single quantum dot (QD) coupled to a pillar microcavity [Nat. Nanotechnol. 12, 663 (2017)], we put forward an alternative setup for the generation of orthogonally polarized dual frequency combs and their corresponding control by using coherent two-tone cavity driving, i.e., a control laser and a probe laser. The present QD-pillar microcavity system operates in the weak-coupling regime, and this makes the experimental realization of the scheme easy. The underlying nonlinear process of the system, thanks to the QD-pillar interaction, for example, degenerate and nondegenerate four-wave mixing, results in efficient frequency comb formation. The dual combs consist of equidistant spectral lines whose spectral spacing coincides with the frequency difference between the control and probe lasers. So, programming this frequency difference between them enables us to tune both the comb-line spacing (i.e., repetition rate) and comb-line number in both vertical ($V$) and horizontal ($H$) polarizations. As compared with the previous approaches for dual microcomb generation, the present scheme has attractive features such as a tunable, slow repetition rate (as slow as a few megahertz), low input power (as low as a few nanowatts), and integrated compact nature in experimentally realistic operating regimes. The achievable low repetition rates are desirable to resolve narrower spectral lines and to enable use of low-power signal processing electronics.

Generation of optical vortices by exciton polaritons in pillar semiconductor microcavities.

We propose a scheme to generate optical vortices through exciting exciton polariton vortices by a Gaussian beam in a pillar microcavity. With coupled Gross-Piteavskii equations we find that the structure of the exciton polariton vortices and antivortices shows a strong dependence on the microcavity radius, pump geometry, and nonlinear exciton-exciton interaction. Due to the nonlinear exciton-exciton interaction the strong Gaussian beam cannot excite more exciton polariton vortices or antivortices with respect to the weak one. The calculation demonstrates that the weak Gaussian beam can excite vortex-antivortex pairs, vortices with high total orbital angular momentum, and superposition states of vortex and antivortex with high total opposite orbital angular momentum. The pump geometry for the Gaussian beam to excite these vortex structures is analyzed in detail, which shows a potential application for generating optical vortex beams.

Photon-Number-Resolved Measurement of an Exciton-Polariton Condensate.

We measure the full photon-number distribution emitted from a Bose condensate of microcavity exciton polaritons confined in a micropillar cavity. The statistics are acquired by means of a photon-number-resolving transition edge sensor. We directly observe that the photon-number distribution evolves with the nonresonant optical excitation power from geometric to quasi-Poissonian statistics, which is canonical for a transition from a thermal to a coherent state. Moreover, the photon-number distribution allows one to evaluate the higher-order photon correlations, shedding further light on the coherence formation and phase transition of the polariton condensate. The experimental data are analyzed in terms of thermal-coherent states, which gives direct access to the thermal and coherent fraction from the measured distributions. These results pave the way for a full understanding of the contribution of interactions in light-matter condensates in the coherence buildup at threshold.

Resonant Edge‐State Switching in Polariton Topological Insulators

AbstractTopological insulators are unique devices supporting unidirectional edge states at their interfaces. Due to topological protection, such edge states persist in the presence of disorder and do not experience backscattering upon interaction with defects. Despite the topological protection and the fact that such states at the opposite edges of an insulator carry opposite currents, a physical mechanism exists allowing topological excitations propagating at opposite edges to be resonantly coupled. Such a mechanism uses weak periodic temporal modulations of the system parameters and does not affect the internal symmetry and topology of the system. This mechanism is illustrated in truncated honeycomb arrays of microcavity pillars, where topological insulation is possible for polaritons under the combined action of spin–orbit coupling and Zeeman splitting in the external magnetic field. The temporal modulation of the potential leads to a periodic switching between topological states with the same Bloch momentum, but located at the opposite edges. The switching rate is found to increase for narrower ribbon structures and for larger modulation depth, though it is changing nonmonotonically with the Bloch momentum of the input edge state. These results provide a promising realization of a coupling device based on topologically protected states.