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We study the interaction between a probe and a trigger weak fields in a sample of cold rubidium atoms in the presence of a coupling and a dressing strong fields. Dipole Rydberg blockade may occur and can be set to depend on the probe and trigger polarizations giving rise to diverse regimes of electromagnetically induced transparency (EIT) with a concomitant small probe and trigger absorption and dispersion. This is shown to be relevant to the implementation of polarization conditional probe and trigger cross nonlinearities in cold Rydberg atoms.

A theory for the electron (and hole) $g$ factor in multivalley lead-salt IV-VI semiconductor quantum wells (QWs) is presented. An effective Hamiltonian for the QW electronic states in the presence of an external magnetic field is introduced within the envelope-function approximation, based on the multiband $kp$ Dimmock model for the bulk. The mesoscopic spin-orbit (Rashba-type) and Zeeman interactions are taken into account on an equal footing and the effective $g$ factor in symmetric quantum wells (${g}_{\mathrm{QW}}^{*}$) is calculated analytically for each nonequivalent conduction-band (and valence-band) valley, and for QWs grown along different crystallographic directions.

Light propagation in optical lattices of driven cold atoms exhibits non-Hermitian degeneracies when the first-order modulation amplitudes of real and imaginary parts of the probe susceptibility are manipulated to be balanced. At these degeneracies, one may observe complete unidirectional reflectionless light propagation. This strictly occurs with no gain and can be easily tuned and fully reversed as supported by the transfer-matrix calculations and explained via a coupled-mode analysis.

We theoretically study how the phase of a light plane wave propagating in a resonant medium under electromagnetically induced transparency (EIT) is affected by the uniform motion of the medium. For cuprous oxide (Cu2O), where EIT can be implemented through a typical pump-probe configuration, the resonant probe beam experiences a phase shift (Fresnel-Fizeau effect) that may vary over a wide range of values, positive or negative, and even vanishing, due to the combined effects of the strong frequency dispersion and anisotropy both induced by the pump. The use of such a coherently driven dragging medium may improve by at least 1 order of magnitude the sensitivity at low velocity in optical drag experiments.

We study the microcavity effect on energy transfer via the electromagnetic field. The modification of the optical propel ties of the microcavity due to the presence of absorbing accepters is taken into account. We analyze different cases that may be realized depending on the characteristics of the acceptor absorption band: the case of strong and broad absorption, when the cavity mode is practically destroyed; the regime of weak absorption, when the cavity mode is still well defined and just acquires some additional broadening; and the strong-coupling regime, when the acceptor absorption has the shape of a strong and narrow peak and two polariton branches appear, formed due to coherent mixing of the acceptor excitations and the cavity mode. In our calculations we use a realistic model for the cavity mirrors (dielectric or metallic), which is important since the mirrors introduce an additional decay channel for the donor excitation besides the transfer to the accepters. The distribution of the energy between different decay channels is analyzed in detail.

We propose to engineer the atomic band structure in optical lattices in order to design a Fabry-Perot interferometer with large mode spacing and strong nonlinear coupling to be employed in atom optics. The use of an optical lattice allows for a significant reduction of the atomic effective mass, while the slow modulation of its parameters spatially confines the matter waves on a length scale of a few dozen optical wavelengths. As a consequence, the mode spacing in such a cavity would be as high as one-tenth of the recoil energy, allowing for a very efficient filter action, while the nonlinear coupling due to interatomic interactions could lead to bistability and limiting effects in the transmission of the atomic beam.

Polariton lasing has recently been observed in strongly coupled crystalline anthracene microcavities. A simple model is developed describing the onset of the non-linear threshold based on a master equation including the relevant relaxation processes and employing realistic material parameters. The mechanism governing the build-up of the polariton population - namely bosonic stimulated scattering from the exciton reservoir via a vibronically assisted process - is characterized and its efficiency calculated on the basis of a microscopic theory. The role of polariton-polariton bimolecular quenching is identified and temperature dependent effects are discussed., Comment: 7 pages main text plus 3 appendices. 10 figures

The localized vibrational modes of the 3d transition-metal ions (TMI's) substituting for the cations in CdTe, ZnTe, and CdSe appear in infrared absorption with as many lines as there are isotopes of the impurity and with intensities proportional to their natural abundances. The triply degenerate local mode in a zinc-blende host splits into a singlet and a doublet in a wurtzite host, the former appearing only when the electric vector (E) of the incident radiation is parallel to the optic axis ((c) over cap) and the latter when . Replacement of Cd by a TMI in CdSe results in high-frequency local vibrational as well as gap modes lying in the gap between the acoustic- and optic-phonon branches, the latter exhibiting an optical anistropy similar to that of the former. Both the local and the gap modes exhibit a unique nonmonotonic trend across the 3d transition-metal series, with a minimum at Mn.

We theoretically consider a hybrid heterostructure made of an inorganic quantum well in close proximity with an organic material overlayer whereby the latter is used to funnel excitation energy to the former in order to exploit the optical nonlinearities of the two-dimensional Wannier excitons. On the one hand, the diffusion length of Frenkel excitons in the organic medium is assumed to be comparable or larger than the corresponding absorption length. On the other hand, the nonradiative energy transfer from the organic to the inorganic subsytem can be very efficient when the Frenkel exciton energy is significantly higher than the band gap of the inorganic semiconductor. We show in this regime that the resonant optical pumping of the Frenkel excitons can lead to an efficient indirect pumping of the Wannier excitons (or electron-hole plasma) in the inorganic quantum well turning on the corresponding nonlinearities.

A spin-dependent variational theory is used to analyze the Rashba spin-orbit splitting in two-dimensional electron gases formed in III--V semiconductor inversion layers. The spin split conduction subbands in CdTe/InSb, insulator/InAs, InP/InGaAs, InAlAs/InGaAs, and AlGaAs/GaAs heterojunctions are calculated. The theory, presented here in detail, is based on the 8 $\ifmmode\times\else\texttimes\fi{}$ 8 $\mathbf{k}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{p}$ Kane model and on the introduction of simple and convenient spin-dependent Fang-Howard trial functions, and leads to analytical expressions for the split subbands, as well as allows for a detailed knowledge of the Rashba spin-orbit coupling, including its explicit dependence on structure parameters and its decomposition into separate contributions. The Rashba coupling parameter and the population difference in the spin-split subbands, as experimentally determined from the beating pattern of the Shubnikov-de Haas (SdH) oscillations, are obtained as a function of the electron density (${n}_{s}$). The separate contributions to the particularly large Rashba splitting in CdTe/InSb heterojunctions are also computed and discussed. It is shown, for example, that due to the spin-dependent boundary conditions, the direct Rashba spin-orbit coupling term in the effective Hamiltonian dominates the splitting only for ${n}_{s}g{10}^{10}$ cm${}^{\ensuremath{-}2}$ while it is the barrier penetration kinetic energy term that gives the largest contribution to the Rashba effect at lower densities.

Layered systems (e.g., semiconductor superlattices) with a deterministic nonperiodic structure exhibit characteristic lengths at all scales, therefore their properties are especially interesting in the infinite limit. X-ray-diffraction spectra of such systems are usually analyzed in terms of their Fourier transforms, i.e., within the kinematical theory of scattering. The diffraction pattern of an infinite lattice, though, is rigorously described only by the dynamical theory of scattering which, in particular, takes multiple reflections and extinction into account. As an example, the diffraction pattern of the Thue-Morse lattice is studied theoretically in the infinite limit. The results of high-resolution x-ray diffraction measurements on a GaAs-AlAs Thue-Morse superlattice are presented and analyzed. Photoluminescence and photoluminescence excitation spectra of the same structure are also discussed.

Radiative lifetimes are measured for excitons attached to isolated (001) InAs lattice planes interspersed in bulklike GaAs. The broken translational invariance of the system provides an efficient radiative decay channel for excitons. We demonstrate that the radiative lifetime is determined by the spatial extent of areas of continuous In coverage. This dependence directly indicates the superradiant nature of the spontaneous-emission process, since the decay rate is proportional to the area over which the coherent polarization of the exciton extends.

Control of the Rashba spin-orbit coupling in semiconductor two-dimensional electron gases (2DEGs) is of fundamental interest to the rapidly evolving semiconductor spintronics and depends on the detailed knowledge of the controversial interface and barrier penetration effects. Based on the $8\ifmmode\times\else\texttimes\fi{}8$ $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ Kane model for the bulk, we propose a spin-dependent variational solution for the conduction subbands of III-V heterojuctions, which reveals analytically the different contributions to the Rashba splitting and its dependency on heterostructure and band parameters as the band offset and effective masses. Perturbation expansions are used to derive renormalized parameters for an effective, simple, and yet accurate one band model. Spin-dependent modified Fang-Howard trial functions, which satisfy the spin-dependent boundary conditions, are then introduced. The subband splitting is given as a function of the variational parameter which is obtained minimizing the total energy of the 2DEG. Our calculations applied to InAlAs/InGaAs heterojunctions, where a near 20% increase in the splitting is observed due to the barrier penetration, are in good agreement with both experiment and exact numerical calculations. Well-known expressions in the limit of a perfect insulating barrier are exactly reproduced.

We have developed a model accounting for the photo-excitation dynamics and the photoluminescence of strongly coupled J-aggregate microcavities. Our model is based on a description of the J-aggregate film as a disordered Frenkel exciton system in which relaxation occurs due to the presence of a thermal bath of molecular vibrations. In a strongly coupled microcavity exciton-polaritons are formed, mixing superradiant excitons and cavity photons. The calculation of the microcavity steady-state photoluminescence, following a CW non resonant pumping, is carried out. The experimental photoluminescence intensity ratio between upper and lower polariton branches is accurately reproduced. In particular both thermal activation of the photoluminescence intensity ratio and its Rabi splitting dependence are a consequence of the bottleneck in the relaxation, occurring at the bottom of the excitonic reservoir. The effects due to radiative channels of decay of excitons and to the presence of a paritticular set of discrete optical molecular vibrations active in relaxation processes are investigared., Comment: 8 pages, 6 figures

We describe an application of the x-ray-standing-wave technique to analyzing noncommensurate surface adsorbate structures. Coherent fractions larger than zero are generally expected if the adsorbate reflects the substrate surface corrugation or potential. We explicitly calculate standing-wave results for an in-plane incommensurate, corrugated adsorbate and for a two-dimensional lattice gas, using a model adsorbate-substrate interaction potential.

Inhomogeneously broadened optical transitions of nitrogen-vacancy centers in diamond may be employed to attain fully developed photonic band-gap structures with negligible absorption via coherent optical nonlinearities. For realistic material parameters, the resulting band gap may be tuned via the coupling field to acquire reflectivities very close to unity and sufficiently large bandwidths. We anticipate that this can be used to optically control with remarkable experimental simplicity the reflected and transmitted parts of an incident light pulse.

We study the optical transitions and their relation to the crystal potential in ultrathin InAs/GaAs multiple quantum wells. Photoluminescence, photoluminescence excitation, and photoreflectance measurements evidence strong localization of the heavy- and light-hole excitons in submonolayer wide InAs quantum wells. A tight-binding model in the linear-chain approximation explains these results in terms of particle localization at the two-dimensional potential discontinuity produced by the insertion of the InAs plane in the host GaAs matrix.

A calculation of the amplitude for longitudinal-optical phonon scattering between hole Landau levels induced by the Fr\"ohlich interaction is presented. This amplitude, forbidden in the dipole approximation, is proportional to (${\mathit{qR}}_{0}$${)}^{2}$ in the limit of high magnetic field, where ${\mathit{R}}_{0}$ is the Landau length and q the phonon wave vector along the magnetic field. The interband Fr\"ohlich scattering brings about double resonances, observable in magneto-Raman spectra, which are comparable to those induced by the deformation-potential interaction. Such resonances have been experimentally studied in GaAs with backscattering Faraday configurations with q along a cubic axis.

We study hybrid organic-inorganic microcavities in the strong coupling regime. The optically resonant materials are an organic monolayer and a semiconductor quantum well, which are spatially separated and coupled only via the cavity photons. The hybrid cavity eigenmodes are hybrid Frenkel-Wannier-Mott exciton polaritons. We derive the nonlinear hybrid polariton-polariton interactions, which stem from the Frenkel and Wannier-Mott exciton-exciton interactions in the organic and inorganic materials, respectively. We show that such a hybrid interaction strength can be controlled by changing the exciton and cavity photon detuning energies. The linear and nonlinear response functions of a hybrid microcavity for an external field are obtained with resonances at the hybrid polariton frequencies.

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.

We consider crystalline organic microcavities in the strong coupling regime. Using a microscopic theory to describe the Frenkel excitons and their coupling to the cavity photon modes, we derive the cavity exciton-polariton dispersion relations and quantum states, for the two cases of anisotropic organic crystals with one and two molecules per unit cell. In the most general case, the cavity exciton polaritons are a coherent superposition of both Davydov exciton branches and of both cavity mode polarizations. The polarization mixing, which occurs also in the case of a single molecule per unit cell, is in contrast to the case of typical inorganic semiconductor cavities in which TM and TE polarizations do not mix. We derive the transmission, reflection, and absorption coefficients for organic cavities by applying the quasimode approximation for high quality cavities. The crossed polarized spectra, e.g., the TM polarized reflected light for TE polarized incident light, clearly show the optical anisotropy of organic microcavities in the regime of strong coupling.

In typical organic based microcavities, large values of Rabi splitting are accompanied by any amount of structural disorder. We present a microscopic approach which treats on equal footing the strong light-matter coupling and the disorder scattering which breaks translational symmetry. Through direct numerical diagonalization in a long, but finite, disordered one-dimensional microcavity, the nature of the eigenstates is elucidated and compared to that of the plane-wave-like cavity polaritons of a perfect system. It is shown that delocalized states with well defined wave vectors or strongly localized states may occur, depending on their energy. In particular, at energies close to the excitonic resonance as well as at the bottom of the polariton branches, the states are definitely not plane-wave-like.

We study the dynamics of a single Frenkel exciton in a disordered molecular chain. The coherent-potential approximation (CPA) is applied to the situation when the single-molecule excitation energies as well as the transition dipole moments, both their absolute values and orientations, are random. Such model is believed to be relevant for the description of the linear optical properties of one-dimensional $J$ aggregates. We calculate the exciton density of states, the linear absorption spectra and the exciton coherence length which reveals itself in the linear optics. A detailed analysis of the low-disorder limit of the theory is presented. In particular, we derive asymptotic formulas relating the absorption linewidth and the exciton coherence length to the strength of disorder. Such expressions account simultaneously for all the above types of disorder and reduce to well-established form when no disorder in the transition dipoles is present. The theory is applied to the case of purely orientational disorder and is shown to agree well with exact numerical diagonalization., Comment: RevTeX4, 17 pages, 9 figures

We theoretically investigate the transmission dynamics of coherent matter wave pulses across finite optical lattices in both the linear and the nonlinear regimes. The shape and the intensity of the transmitted pulse are found to strongly depend on the parameters of the incident pulse, in particular its velocity and density: a clear physical picture for the main features observed in the numerical simulations is given in terms of the atomic band dispersion in the periodic potential of the optical lattice. Signatures of nonlinear effects due the atom-atom interaction are discussed in detail, such as atom optical limiting and atom optical bistability. For positive scattering lengths, matter waves propagating close to the top of the valence band are shown to be subject to modulational instability. A new scheme for the experimental generation of narrow bright gap solitons from a wide Bose-Einstein condensate is proposed: the modulational instability is seeded in a controlled way starting from the strongly modulated density profile of a standing matter wave and the solitonic nature of the generated pulses is checked from their shape and their collisional properties.

We theoretically study the elastic scattering of lower cavity polaritons on the static disorder in high quality semiconductor microcavities in the strong coupling regime. We consider the dominant contribution of the resonant scattering on localized exciton levels and calculate for a model density of states the corresponding elastic mean free path. Our analytical results compare well with available linewidth data and substantiate the possibility of weak localization.

We present a study of the effect of uniaxial stress on the electric-dipole spin resonance absorption in zinc-blende semiconductors. We show that previous work in this field omits an important contribution to the transition amplitude, leading to an underestimate of the strength ${C}_{2}$ of the stress-induced spin-orbit coupling in InSb. The necessary correction factor is between 3 and 4. We suggest experimental configurations that would permit an accurate measurement of this and other related material parameters. One of these exploits the possibility of an interference between stress-induced and stress-free spin-flip transition amplitudes. In this way, not only the magnitude of ${C}_{2}$, but also its sign, could be determined.