Polarization Dependent Scattering in Cavity Optomagnonics.

The polarization dependence of magnon-photon scattering in an optical microcavity is reported. Because of the short cavity length, the longitudinal mode-matching conditions found in previously explored, large path-length whispering gallery resonators are absent. Nonetheless, for cross-polarized scattering a strong and broadband suppression of one sideband is observed. This arises due to an interference between the Faraday and second-order Cotton-Mouton effects. To fully account for the suppression of the cross-polarized scattering, it is necessary to consider the squeezing of magnon modes intrinsic to thin-film geometry. A copolarized scattering due to Cotton-Mouton effect is also observed. In addition, the magnon modes involved are identified as Damon-Eshbach surface modes, whose nonreciprocal propagation could be exploited in device applications. This Letter experimentally demonstrates the important role of second-order Cotton-Mouton effect for optomagnonic devices.

Spin Order and Phase Transitions in Chains of Polariton Condensates.

We demonstrate that multiply coupled spinor polariton condensates can be optically tuned through a sequence of spin-ordered phases by changing the coupling strength between nearest neighbors. For closed four-condensate chains these phases span from ferromagnetic (FM) to antiferromagnetic (AFM), separated by an unexpected crossover phase. This crossover phase is composed of alternating FM-AFM bonds. For larger eight-condensate chains, we show the critical role of spatial inhomogeneities and demonstrate a scheme to overcome them and prepare any desired spin state. Our observations thus demonstrate a fully controllable nonequilibrium spin lattice.

Triple-Resonant Brillouin Light Scattering in Magneto-Optical Cavities.

An enhancement in Brillouin light scattering of optical photons with magnons is demonstrated in magneto-optical whispering gallery mode resonators tuned to a triple-resonance point. This occurs when both the input and output optical modes are resonant with those of the whispering gallery resonator, with a separation given by the ferromagnetic resonance frequency. The identification and excitation of specific optical modes allows us to gain a clear understanding of the mode-matching conditions. A selection rule due to wave vector matching leads to an intrinsic single-sideband excitation. Strong suppression of one sideband is essential for one-to-one frequency mapping in coherent optical-to-microwave conversion.

Optical spin-transfer-torque-driven domain-wall motion in a ferromagnetic semiconductor.

We demonstrate optical manipulation of the position of a domain wall in a dilute magnetic semiconductor, GaMnAsP. Two main contributions are identified. First, photocarrier spin exerts a spin-transfer torque on the magnetization via the exchange interaction. The direction of the domain-wall motion can be controlled using the helicity of the laser. Second, the domain wall is attracted to the hot spot generated by the focused laser. Unlike magnetic-field-driven domain-wall depinning, these mechanisms directly drive domain-wall motion, providing an optical tweezerlike ability to position and locally probe domain walls.

Phonon-assisted population inversion of a single InGaAs/GaAs quantum dot by pulsed laser excitation.

We demonstrate a new method to realize the population inversion of a single InGaAs/GaAs quantum dot excited by a laser pulse tuned within the neutral exciton phonon sideband. In contrast to the conventional method of inverting a two-level system by performing coherent Rabi oscillation, the inversion is achieved by rapid thermalization of the optically dressed states via incoherent phonon-assisted relaxation. A maximum exciton population of 0.67±0.06 is measured for a laser tuned 0.83 meV to higher energy. Furthermore, the phonon sideband is mapped using a two-color pump-probe technique, with its spectral form and magnitude in very good agreement with the result of path-integral calculations.

Inverse conoscopy: a method to measure polarization using patterns generated by a single birefringent crystal.

A method to measure the full polarization vector of a laser beam is proposed and demonstrated. Light is focused onto a birefringent crystal cut such that the slow axis is aligned with the optical axis. The polarization vector of each ray experiences a rotation about the radial axis with a retardation phase dependent on the angle of incidence. Illumination over a wide range of angles applies a range of polarization transforms in parallel that generates a distinct pattern detected by a camera. The input polarization is then inferred from the pattern. The setup uses a single birefringent crystal and involves no moving parts.

Interfacing spins in an InGaAs quantum dot to a semiconductor waveguide circuit using emitted photons.

An in-plane spin-photon interface is essential for the integration of quantum dot spins with optical circuits. The optical dipole of a quantum dot lies in the plane and the spin is optically accessed via circularly polarized selection rules. Hence, a single waveguide, which can transport only one in-plane linear polarization component, cannot communicate the spin state between two points on a chip. To overcome this issue, we introduce a spin-photon interface based on two orthogonal waveguides, where the polarization emitted by a quantum dot is mapped to a path-encoded photon. We demonstrate operation by deducing the spin using the interference of in-plane photons. A second device directly maps right and left circular polarizations to antiparallel waveguides, surprising for a nonchiral structure but consistent with an off-center dot.

Fast control of nuclear spin polarization in an optically pumped single quantum dot.

Highly polarized nuclear spins within a semiconductor quantum dot induce effective magnetic (Overhauser) fields of up to several Tesla acting on the electron spin, or up to a few hundred mT for the hole spin. Recently this has been recognized as a resource for intrinsic control of quantum-dot-based spin quantum bits. However, only static long-lived Overhauser fields could be used. Here we demonstrate fast redirection on the microsecond timescale of Overhauser fields on the order of 0.5 T experienced by a single electron spin in an optically pumped GaAs quantum dot. This has been achieved using coherent control of an ensemble of 10(5) optically polarized nuclear spins by sequences of short radiofrequency pulses. These results open the way to a new class of experiments using radiofrequency techniques to achieve highly correlated nuclear spins in quantum dots, such as adiabatic demagnetization in the rotating frame leading to sub-µK nuclear spin temperatures, rapid adiabatic passage, and spin squeezing.

Coherent optical control of the spin of a single hole in an InAs/GaAs quantum dot.

We demonstrate coherent optical control of a single hole spin confined to an InAs/GaAs quantum dot. A superposition of hole-spin states is created by fast (10-100 ps) dissociation of a spin-polarized electron-hole pair. Full control of the hole spin is achieved by combining coherent rotations about two axes: Larmor precession of the hole spin about an external Voigt geometry magnetic field, and rotation about the optical axis due to the geometric phase shift induced by a picosecond laser pulse resonant with the hole-trion transition.

Interleukin 5 deficiency abolishes eosinophilia, airways hyperreactivity, and lung damage in a mouse asthma model.

Airways inflammation is thought to play a central role in the pathogenesis of asthma. However, the precise role that individual inflammatory cells and mediators play in the development of airways hyperreactivity and the morphological changes of the lung during allergic pulmonary inflammation is unknown. In this investigation we have used a mouse model of allergic pulmonary inflammation and interleukin (IL) 5-deficient mice to establish the essential role of this cytokine and eosinophils in the initiation of aeroallergen-induced lung damage and the development of airways hyperreactivity. Sensitization and aerosol challenge of mice with ovalbumin results in airways eosinophilia and extensive lung damage analogous to that seen in asthma. Aeroallergen-challenged mice also display airways hyperreactivity to beta-methacholine. In IL-5-deficient mice, the eosinophilia, lung damage, and airways hyperreactivity normally resulting from aeroallergen challenge were abolished. Reconstitution of IL-5 production with recombinant vaccinia viruses engineered to express this factor completely restored aeroallergen-induced eosinophilia and airways dysfunction. These results indicate that IL-5 and eosinophils are central mediators in the pathogenesis of allergic lung disease.

Damping of exciton Rabi rotations by acoustic phonons in optically excited InGaAs/GaAs quantum dots.

We report experimental evidence identifying acoustic phonons as the principal source of the excitation-induced-dephasing (EID) responsible for the intensity damping of quantum dot excitonic Rabi rotations. The rate of EID is extracted from temperature dependent Rabi rotation measurements of the ground-state excitonic transition, and is found to be in close quantitative agreement with an acoustic-phonon model.

Phonon-induced Rabi-frequency renormalization of optically driven single InGaAs/GaAs quantum dots.

We study optically driven Rabi rotations of a quantum dot exciton transition between 5 and 50 K, and for pulse areas of up to 14π. In a high driving field regime, the decay of the Rabi rotations is nonmonotonic, and the period decreases with pulse area and increases with temperature. By comparing the experiments to a weak-coupling model of the exciton-phonon interaction, we demonstrate that the observed renormalization of the Rabi frequency is induced by fluctuations in the bath of longitudinal acoustic phonons, an effect that is a phonon analogy of the Lamb shift.

The role of interleukin-6 in mucosal IgA antibody responses in vivo.

In mice with targeted disruption of the gene that encodes interleukin-6 (IL-6), greatly reduced numbers of immunoglobulin A (IgA)-producing cells were observed at mucosae and grossly deficient local antibody responses were recorded after mucosal challenge with either ovalbumin or vaccinia virus. The IgA response in the lungs was completely restored after intranasal infection with recombinant vaccinia viruses engineered to express IL-6. These findings demonstrate a critical role for IL-6 in vivo in the development of local IgA antibody responses and illustrate the effectiveness of vector-directed cytokine gene therapy.

Aeroallergen-induced eosinophilic inflammation, lung damage, and airways hyperreactivity in mice can occur independently of IL-4 and allergen-specific immunoglobulins.

In this investigation we have used a mouse model containing certain phenotypic characteristics consistent with asthma and IL-4- and CD40-deficient mice to establish the role of this cytokine and allergen-specific immunoglobulins in the initiation of airways hyperreactivity and morphological changes to the airways in responses to aeroallergen challenge. Sensitization and aerosol challenge of mice with ovalbumin resulted in a severe airways inflammatory response which directly correlated with the induction of extensive airways damage and airways hyperreactivity to beta-methacholine. Inflammatory infiltrates were primarily characterized by the presence of CD4+ T cells and eosinophils. In IL-4-deficient mice, the recruitment of airways eosinophils was impaired, but not abolished in response to aeroallergen. Moreover, the characteristic airways damage and hyperreactivity normally resulting from allergen inhalation were not attenuated. Induction of these structural and functional changes to the airways occurred in the absence of ovalbumin-specific IgE and IgG1, but IgG2a and IgG3 were detected in the sera of IL-4-deficient mice. CD4+ T cells isolated from both wild-type and IL-4-deficient mice given ovalbumin produced significant levels of IL-5 after in vitro stimulation. Treatment of IL-4-deficient mice with anti-IL-5 mAb before aeroallergen challenge abolished blood and airways eosinophilia, lung damage, and airways hyperreactivity. These results indicate that IL-4 is not essential for the development of IL-5-producing CD4+ T cells or for the induction of eosinophilic inflammation and airways damage and hyperreactivity. In response to sensitization and aerosol challenge, CD40-deficient mice did not produce ovalbumin-specific IgE, IgG isotypes, or IgA, and airways inflammation and hyperreactivity were not attenuated. Our results suggest that allergic airways disease can occur via pathways which operate independently of IL-4 and allergen-specific immunoglobulins. Activation of these pathways is intimately associated with IL-5 and eosinophilic inflammation. Such pathways may play a substantive role in the etiology of asthma.

Cytokine responses in virus infections: effects on pathogenesis, recovery and persistence.

During the past year, significant advances have been made in our understanding of cytokine regulation and the respective roles played by T helper cells type 1 and 2 immune responses during virus infection. Numerous mechanisms by which viruses may evade host immune defences have now been identified, some directly influencing cytokine activity. Major advances have also been made in delineating the roles of cytokines and chemokines at different stages in the pathogenesis of HIV infection.

Interleukin-7 enhances cell-mediated immune responses in vivo in an interleukin-2-dependent manner.

We have engineered recombinant vaccinia virus vectors expressing murine interleukin-7 (IL-7) in order to study the activity of this factor during virus infection. Virus-encoded IL-7 dramatically increased splenic cellularity in infected mice and enhanced the proliferative activity of T cells and their capacity to secrete IL-2 and IL-6, but not IFN-gamma, TNF-alpha or IL-4. Numbers of splenic CD4+ and CD8+ T lymphocytes were elevated two- to threefold. IL-7 also mediated a marked enhancement of both antigen-specific and nonspecific cellular immune activity. Total splenic antiviral cytotoxic T cells (CTL), natural killer (NK), and lymphokine-activated killer cells (LAK) responses were augmented significantly in mice given VV-HA-IL-7 compared with those given control virus, with accelerated clearance of the former. The enhanced antiviral cellular immune activity mediated by IL-7 was critically dependent on IL-2 produced by the host, but occurred independently of IFN-gamma. The ability of IL-7 to induce cellular immune responses in vivo may have applications in antiviral immunotherapy, particularly in cases of immunodeficiency.

Antigen delivery strategies for mucosal vaccines.

Progress towards effective vaccines to control internal parasites, especially those affecting mucosal compartments, has been inhibited by the combined problems of the antigenic complexity of parasites and the lack of understanding of the host response. However, the accumulation of information regarding regulation of mucosal immunity has enabled a reappraisal of vaccination options to provide appropriate mucosal effector responses. The pivotal role of T cell influences, and in particular the contribution of cytokine signals, has been clearly established from in vitro studies, but data emerging from our laboratories provide evidence for these effects in vivo. We have demonstrated the role of T cells in determining the outcome of an intestinal response and propose a role for local Th2 cytokine production in this regard. To support this proposition, the distribution of cytokine mRNA has been determined by in situ hybridisation techniques in normal and parasitised animals. Further, we have shown that in the absence of Th2 cytokines (using gene knockout animals) mucosal responses are grossly deficient; we have also shown that this defect can be overcome by vector-directed gene therapy. These studies have indicated that new mucosal immunisation opportunities exist by combining traditional immunisation approaches with strategies to upregulate local cytokine production. However, the success of these new strategies will depend on selection of highly immunogenic subunit antigens, coupled with techniques for cytokine manipulation and delivery with appropriate adjuvant/vehicle formulations. This paper reviews delivery technologies available to chaperone labile antigenic and genetic material to appropriate sites for mucosal stimulation after systemic or oral administration.

Cytokine enhancement of immune responses important for immunocontraception.

To be effective, an immunocontraceptive vaccine should elicit strong, sustained antibody responses. Circulating antibodies may block the function of hormones and target some gamete antigens, but the most effective inhibition of fertilization will probably be achieved by antibodies in the reproductive tract. It may also be beneficial to administer vaccine antigens with strong adjuvants, such as cytokines, in order to achieve high specific antibody titres. In this review recent findings concerning the role of cytokines in the regulation of antibody responses, particularly at mucosae, are described and prospects for immunization for immune responses which may be important for fertility control are discussed. On the basis of these findings, a model system for the delivery of vaccine antigens to the immune system in vaccinia, fowlpox or DNA plasmid vectors along with type-2 cytokines, such as interleukin-4 (IL-4), IL-5 and IL-6, as B cell adjuvants is presented. Studies such as these in the areas of antigen delivery and enhancement of immune responses are aimed at providing new options for fertility control, particularly via oral vaccination.

Cytokine regulation of mucosal responses: a rational basis for new vaccine delivery strategies.

In this review, cytokine regulation of mucosal responses is discussed in relation to the mucosal immune network and regulation of IgA responses. Based on this understanding, aspects of gene therapy for manipulation of the host environment and vaccine delivery systems are discussed. Although evidence obtained in vitro is briefly reviewed the general focus of this article is on evidence obtained from models in vivo.

Enhancement of mucosal IgA responses by interleukins 5 and 6 encoded in recombinant vaccine vectors.

The expression of the genes for murine interleukin-5 (IL-5) or IL-6 in recombinant vaccinia virus vectors markedly increased IgA reactivity to co-expressed heterologous antigen in the lungs of mice inoculated intranasally with the viruses. These elevated local IgA responses reached a peak four times higher than those elicited by control viruses 14 days after infection and these peak levels were maintained for at least four weeks. Elevated IgA responses, reaching a peak 3-4 weeks after immunization, were also observed in the lungs of mice inoculated with IL-6 expressed by another vector, fowlpox virus. The results indicate that these factors enhance the development of mucosal IgA reactivity in vivo and suggest that their expression in mucosal vaccine vectors may stimulate local immune responses. The approach described in this study may be useful in stimulating mucosal immunity to a wide range of vector-encoded antigens, not only for vaccination against disease but also for immunocontraception by the co-expression of antigens involved in reproduction.