Cavity Semiconductor Research Articles

Photon antibunching in strongly coupled exciton–semiconductor cavity systems: Role of off-resonant coupling to multiple excitons

We present a master equation approach to study the second-order quantum autocorrelation functions for up to two quantum-dot excitons, coupled to an off-resonant cavity in a semiconductor-single quantum-dot cavity system. For a single coupled off-resonant exciton, we observe unusual oscillatory behavior in the early time dynamics of the cavity autocorrelation function, which leads to decreased antibunching relative to the exciton mode. With a second coupled exciton in the system, we find that the magnitude and the lifetime of these oscillations greatly increases, since the cavity is then able to exchange photons with multiple excitonic resonances. These results demonstrate that for incoherent pumping, the ubiquitous two-level atom model completely breaks down and that multiple excitonic resonances act in concert to spoil the antibunching characteristics of the cavity quasimode. We connect these findings to a series of recent surprising experimental results for single quantum dot-semiconductor cavity systems, including photonic crystal systems and micropillar cavities.

Surface-plasmon mode hybridization in subwavelength microdisk lasers

Hybridization of surface-plasmon and dielectric waveguide whispering-gallery modes are demonstrated in a semiconductor microdisk laser cavity of subwavelength proportions. A metal layer is deposited on top of the semiconductor microdisk, the radius of which is systematically varied to enable mode hybridization between surface-plasmon and dielectric modes. The anticrossing behavior of the two cavity mode types is experimentally observed via photoluminescence spectroscopy and optically pumped lasing action at a wavelength of λ∼1.3 μm is achieved at room temperature.

Field localization and enhancement of phase-locked second- and third-order harmonic generation in absorbing semiconductor cavities

We predict and experimentally observe the enhancement by three orders of magnitude of phase mismatched second and third harmonic generation in a GaAs cavity at 650 and 433 nm, respectively, well above the absorption edge. Phase locking between the pump and the harmonics changes the effective dispersion of the medium and inhibits absorption. Despite hostile conditions the harmonics resonate inside the cavity and become amplified leading to relatively large conversion efficiencies. Field localization thus plays a pivotal role despite the presence of absorption, and ushers in a new class of semiconductor-based devices in the visible and uv ranges.

Semiconductor Cavity Quantum Electrodynamics with Single Quantum Dots

Semiconductor cavity quantum electrodynamics (cQED) with single quantum dots as artificial atoms and high quality factor cavies is a rapidly developing research field. Solid state platforms are a prerequisite for more wide spread exploitation of cQED effects, which hold promise for the realization of several key devices for quantum information processing and nano-optoelectronics, like single photon sources or ultra-low threshold lasers. Semiconductor systems are particularly attractive because they offer routes for electrical injection or electro-optical tuning. This talk will mainly focus on the presentation of cQED experiments in high-quality factor micropillar cavities containing semiconductor quantum dots (see Fig. 1). After a general introduction into semiconductor cQED with micropillar cavities, the recent progress made in our group on electrically driven micropillar cavities will be reported [1, 2]. By developing a process for planarizing and contacting quantum dot micropillars we fabricated devices with quality factors up to 16.000 for pillar diameters of 4 μm. Such devices feature pronounced cQED effects, like enhanced spontaneous emission, photon antibunching, high-β lasing and electro-optical tuning in both the weak or strong (see Fig. 2) coupling regime. Spatial determinism in cQED is of major importance for the exploitation of related effects on larger scale or for the realization of more complex device functionalities, e.g. the deterministic photonic coupling of remote quantum dots via spatially separated cavities and waveguides. Another main part of the talk will discuss our recent progress made in the field of device integration of site-controlled quantum dots into photonic crystal as well as micropillar cavities (see Fig. 3) [3, 4].

Bose-Einstein condensation of trapped polaritons in two-dimensional electron-hole systems in a high magnetic field

The Bose-Einstein condensation (BEC) of magnetoexcitonic polaritons in two-dimensional (2D) electron-hole system embedded in a semiconductor microcavity in a high magnetic field $B$ is predicted. There are two physical realizations of 2D electron-hole system under consideration: a graphene layer and quantum well (QW). A 2D gas of magnetoexcitonic polaritons is considered in a planar harmonic potential trap. Two possible physical realizations of this trapping potential are assumed: inhomogeneous local stress or harmonic electric field potential applied to excitons and a parabolic shape of the semiconductor cavity causing the trapping of microcavity photons. The effective Hamiltonian of the ideal gas of cavity polaritons in a QW and graphene in a high magnetic field and the BEC temperature as functions of magnetic field are obtained. It is shown that the effective polariton mass $M_{\rm eff}$ increases with magnetic field as $B^{1/2}$. The BEC critical temperature $T_{c}^{(0)}$ decreases as $B^{-1/4}$ and increases with the spring constant of the parabolic trap. The Rabi splitting related to the creation of a magnetoexciton in a high magnetic field in graphene and QW is obtained. It is shown that Rabi splitting in graphene can be controlled by the external magnetic field since it is proportional to $B^{-1/4}$, while in a QW the Rabi splitting does not depend on the magnetic field when it is strong.

Publisher's Note: “All-optical delay line using semiconductor cavity solitons” [Appl. Phys. Lett. 92, 011101 (2008)

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Cavity mode emission in weakly coupled quantum dot - cavity systems

We study the origin of bright leaky-cavity mode emission and its influence on photon statistics in weakly coupled quantum dot - semiconductor cavity systems, which consist of a planar photonic-crystal and several quantum dots. We present experimental measurements that show that when the system is excited above the barrier energy, then bright cavity mode emissions with nonzero detuning are dominated by radiative recombinations of deep-level defects in the barrier layers. Under this excitation condition, the second-order photon autocorrelation measurements reveal that the cavity mode emission at nonzero detuning exhibits classical photon-statistics, while the bare exciton emission shows a clear partial anti-bunching. As we enter a Purcell factor enhancement regime, signaling a clear cavity-exciton coupling, the relative weight of the background recombination contribution to the cavity emission decreases. Consequently, the anti-bunching behavior is more significant than the bare exciton case - indicating that the photon statistics becomes more non-classical. These measurements are qualitatively explained using a medium-dependent master equation model that accounts for several excitons and a leaky cavity mode.

Light scattering in semiconductor quantum-dot cavity systems

Scattering theory is used to investigate the interaction of a coherent light beam with two distant one-sided semiconductor double micro-cavities. Each cavity contains a single quantum dot charged by one extra electron. The polarization and phase shift of the scattered light is studied as a function of the initial spin state of the two electrons, as well as differences in structural properties of the two cavities. It is shown that the Faraday rotation of the transmitted light is sensitive to electronic and structural properties of the cavities making careful calibration mandatory, when entanglement generation between the electron spin states is to be achieved.

Enhanced Lasing Characteristics of Guided Modes in an Epistructured Hollow Hexagonal Cavity

Lasing characteristics of resonance modes were investigated in simple polygons and hollow hexagonal and square cavities made on an epiwafer with an InGaAsP/InGaAs quantum well gain layer. The center wavelength of the lasing showed a red shift as the cavity shape changed from being square to hexagonal or octagonal owing to a reduced cavity loss. In a hollow hexagonal semiconductor cavity, the lasing of guided modes was observed in which the modes were formed by 18 total reflections of light at both boundaries. Through a comparative study with a hollow square cavity, the cavity loss of guided modes in a hollow hexagonal cavity was found to be considerably reduced.

Theory of quantum light emission from a strongly-coupled single quantum dot photonic-crystal cavity system

We present a rigorous medium-dependent theory for describing the quantum field emitted and detected from a single quantum dot exciton, strongly coupled to a planar photonic crystal nanocavity, from which the exact spectrum is derived. By using simple mode decomposition techniques, this exact spectrum is subsequently reduced to two separate user-friendly forms, in terms of the leaky cavity mode emission and the radiation mode emission. On application to study exciton-cavity coupling in the strong coupling regime, besides a pronounced modification of the usual vacuum Rabi spectral doublet, we predict several new effects associated with the leaky cavity mode emission, including the appearance of an off-resonance cavity mode and a loss-induced on-resonance spectral triplet. The cavity mode emission is shown to completely dominate the emitted spectrum, even for large cavity-exciton detunings, whereby the usual cavity-QED formulas developed for radiation-mode emission drastically fail. These predictions are in qualitative agreement with several "mystery observations" reported in recent experiments, and apply to a wide range of semiconductor cavities.

Dependencies of micro-pillar cavity quality factors calculated with finite element methods

We present simulation results for optical modes in micro-pillar cavities that were computed with the finite element method and that show good agreement with experimental data. By means of this viable tool various influences on the quality factor of the fundamental mode were calculated: Firstly, the light confinement depends strongly on the absorption of the semiconductor cavity material. Here we were able to determine absolute maximum quality factors achievable in a GaAs/AlAs Bragg micro-pillar cavity. Furthermore, small pillar diameters as well as the inclination of pillar sidewalls show critical features with respect to light confinement. Additional effects of the top and bottom Bragg stacks in the pillar were calculated as well.

Donor-donor interaction mediated by cavity photons and its relation to interactions mediated by excitons and polaritons

I report theoretical predictions of two models of donor-donor indirect interaction mediated by photons in zero- and two-dimensional cavities. These results are compared to previously studied cases of indirect interactions mediated by excitons and/or polaritons in bulk semiconductor and two-dimensional cavities. I find that photons mediate an Ising-like interaction between donors in the same manner polaritons do, in contrast to the Heisenberg-like interaction mediated by exciton. For the particular case of a two-dimensional cavity, the model shows that the dependence on distance of the donor-donor coupling constant is the same for photons and polaritons when the donor-donor distance is large. Then, it becomes clear that photons are responsible for the long range behavior of the polariton indirect interaction.

Excitonic dynamics of a quantum dot coupled to a laser-driven semiconductor microcavity

Within the density matrix formalism, we report on the quantum control of the excitonic coherences in quantum dots coupled to a single mode field resonant semiconductor cavity. We use an external classical laser field to drive the dynamical response of the excitonic states. Dissipation mechanisms associated with the cavity field and the excitonic states are explicitly included in the model. Our numerical simulations of the excitonic dynamics are in good agreement with recent experimental reports. Furthermore, we compute and show how to tailor such a dynamics in the presence of the laser field by means of controlling the detuning between the laser and the cavity field frequencies. The results are analyzed with a view to implementing quantum control of local qubit operations.

Local Electrical Detection of Single Nanoparticle Plasmon Resonance

We developed a technique for the local electrical detection of a plasmon resonance in a single metal nanoparticle. A gold nanoparticle is coupled to a GaAs photodetector placed in the particle's near field. Light scattered by the particle is coupled into the semiconductor cavity of the photodetector, providing efficient transduction. Strong multipolar resonances were recorded in the 650-920 nm wavelength range. This local detection technique allows the construction of sensitive nanoscale bioprobes and arrays thereof.

Characteristics of switching dynamics in a semiconductor-based cavity-soliton laser

The switching behavior of a semiconductor cavity soliton laser is experimentally investigated, based on a vertical-cavity surface-emitting laser with frequency-selective feedback. In particular, we show the effect of frequency detuning between cavity solitons and the external injection, the temporal dynamics during ignition and erasure, and characterize the necessary injection pulse width versus its power for successful switching.

Cavity polaritons: Classical behavior of a quantum parametric oscillator

We address theoretically the optical parametric oscillator based on semiconductor cavity exciton polaritons under a pulsed excitation. A ``hyperspin'' formalism is developed which allows, in the case of large number of polaritons, to reduce quantum dynamics of the parametric oscillator wave function to the Liouville equation for the classical probability distribution. Implications for the statistics of polariton ensembles are analyzed.

Frenkel-exciton-polaritons in organic microcavities

We study organic microcavities in the strong coupling regime. The cavity exciton-polariton dispersion relations and quantum states are derived in using a microscopic theory. We consider the two cases of anisotropic organic crystals with one and two molecules per unit cell. In general, the cavity exciton-polaritons are a coherent superposition of both cavity mode polarizations and of both Davydov exciton branches. The obtained polarization mixing is in contrast to the case of typical inorganic semiconductor cavities in which no mixing between the TM and TE polarizations occurs. By applying the quasi-mode approximation, we derive the transmission, reflection, and absorption coefficients for high quality organic cavities.

Vacuum Rabi splitting in semiconductors

The recent development of techniques to produce optical semiconductor cavities of very high quality has prepared the stage for observing cavity quantum-electrodynamic effects in solid-state materials. Among the most promising systems for these studies are semiconductor quantum dots inside photonic crystal, micropillar or microdisk resonators. We review the progress so far in obtaining true quantum-optical strong-coupling effects in semiconductors. We discuss the recent results on vacuum Rabi splitting with a single quantum dot, emphasizing the differences from quantum-well systems. Finally, we propose nonlinear tests for the true quantum limit and speculate about applications in quantum information devices.

Optimal Conditions for Achieving Strong Third-Order Nonlinearity in Semiconductor Cavities

We determine the optimal conditions for achieving strong nonlinearity in semiconductor cavities as a function of the Q factor, coupling constant g , and longitudinal (γ 1 ) and pure transverse (γ 2...

Exciton-polariton kinematic interactions in organic microcavities

We analyze the exciton-exciton and polariton-polariton kinematic interactions in crystalline organic microcavities. The kinematic interactions are derived using the Agranovich-Toshich transformation, which transforms the Frenkel excitons from paulions into bosons. From the calculated exciton-scattering cross section in an organic crystalline monolayer, we find that the scattering due to the exciton-exciton kinematic interaction can be described as the scattering between hard disks. We show that, as in the case of two-dimensional ultracold trapped boson atom gas, excitons in a confined monolayer may behave as a dilute degenerate boson gas at low temperature. In an organic cavity, with an organic crystalline monolayer as a resonant material, we derive the polariton-polariton kinematic interaction, which stems from the polariton excitonic part. We calculate the polariton-scattering cross section due to the polariton-polariton kinematic interaction, and recognize the scattering effective potential. We show that, due to the smallness of the polariton effective mass, polaritons in organic cavities may behave as a dilute degenerate boson gas up to room temperature. The comparison between the polariton-polariton kinematic interaction in organic cavities and the polariton-polariton nonlinear interaction in inorganic semiconductor cavities shows that both interactions are of the same order.