Angular Momenta and Spin-Orbit Interaction of Nonparaxial Light in Free Space

We give an exact self-consistent operator description of the spin and orbital angular momenta, position, and spin-orbit interactions of nonparaxial light in free space. Both quantum-operator formalism and classical energy-flow approach are presented. We apply the general theory to symmetric and asymmetric Bessel beams exhibiting spin- and orbital-dependent intensity profiles. The exact wave solutions are clearly interpreted in terms of the Berry phases, quantization of caustics, and Hall effects of light, which can be readily observed experimentally.Comment: 8 pages, 3 figure

Incoherent excitation and switching of spin states in exciton-polariton condensates

We investigate, theoretically and numerically, the spin dynamics of a two-component exciton-polariton condensate created and sustained by non-resonant spin-polarized optical pumping of a semiconductor microcavity. Using the open-dissipative mean-field model, we show that the existence of well defined phase-locked steady states of the condensate may lead to efficient switching and control of spin (polarization) states with a non-resonant excitation. Spatially inhomogeneous pulsed excitations can cause symmetry breaking in the pseudo-spin structure of the condensate and lead to formation of non-trivial spin textures. Our model is universally applicable to two weakly coupled polariton condensates, and therefore can also describe the behaviour of condensate populations and phases in 'double-well' type potentials

Bistability in Microcavities with Incoherent Optical or Electrical Excitation

We consider a quantum well embedded in a zero-dimensional microcavity with a sub-wavelength grated mirror, where the x-linearly polarized exciton mode is strongly coupled to the cavity photon, while y-polarized excitons remain in the weak coupling regime. Under incoherent optical or electric pumping, we demonstrate polariton bistability associated with parametric scattering processes. Such bistability is useful for constructing polaritonic devices with optical or electrical incoherent pumping.Comment: 5 pages, 3 figure

Tradition as a Homeland to Return to: Transnational Religious Identity of the Post-Soviet Orthodox Jewry

Received 26 April 2021. Accepted 14 May 2021. Published online 9 July 2021.This article highlights the outcome of a long-term field research into the transnational identity of the post-Soviet Orthodox Jewry. It analyzes biographical interviews taken between 2015 and 2018 in St. Petersburg and Minsk to define the religious identity and day-to-day practices of post-Soviet Orthodox Jews. In this article, I argue that the communities of post-Soviet Orthodox Jews is a new socio-cultural phenomenon with no historical prototypes. As to the research methodology, it was a combination of the transnational approach, random choice casestudy targeting post-Soviet Orthodox communities of Orthodox Jewry in large cities, and the biographical method. The backbone of the post-Soviet Orthodox communities of different strains of Judaism was formed in 1990–2008. It is made up of three generations of men and women born in the late 1940s–1960s, mid-1960s–early 1970s, and the 1980s. Each of these generations is characterized by its own unique pattern of observance, the formation of which is directly conditioned by the circumstances of involvement in religious Jewry. The transnational pattern of observance of the Post-Soviet Orthodox Jews involves the model they confronted at the very beginning of their journey, the model they learned in overseas educational institutions or through incoming envoys and rabbis in the country of residence, and the model of balance between the required and possible in the modern post-Christian and post-atheist environment

Instability-induced formation and non-equilibrium dynamics of phase defects in polariton condensates

We study, theoretically and numerically, the onset and development of modulational instability in an incoherently pumped spatially homogeneous polariton condensate. Within the framework of mean-field theory, we identify regimes of modulational instability in two cases: 1) Strong feedback between the condensate and reservoir, which may occur in scalar condensates, and 2) Parametric scattering in the presence of polarization splitting in spinor condensates. In both cases we investigate the instability induced textures in space and time including non-equilibrium dynamics of phase dislocations and vortices. In particular we discuss the mechanism of vortex destabilization and formation of spiraling waves. We also identify the presence of topological defects, which take the form of half-vortex pairs in the spinor case, giving an "eyelet" structure in intensity and dipole type structure in the spin polarization. In the modulationally stable parameter domains, we observe formation of the phase defects in the process of condensate formation from an initially spatially incoherent low-density state. In analogy to the Kibble-Zurek type scaling for nonequilibrium phase transitions, we find that the defect density scales with the pumping rate.Comment: 13 pages, 9 figures, revised manuscript sent to Phys. Rev.

Anomalous dispersion and negative-mass dynamics of exciton polaritons in an atomically thin semiconductor

Dispersion engineering is a powerful and versatile tool that can vary the speed of light signals and induce negative-mass effects in the dynamics of electrons, quasiparticles, and quantum fluids. Here, we demonstrate that dissipative coupling between bound electron-hole pairs (excitons) and photons in an optical microcavity can lead to the formation of exciton polaritons with an inverted dispersion of the lower polariton branch and hence, a negative mass. We perform a direct measurement of the anomalous dispersion in an atomically thin WS$_2$ crystal embedded in a planar microcavity, and demonstrate that the propagation direction of the negative-mass polaritons is opposite to their momentum. Our study introduces a new concept of non-Hermitian dispersion engineering for exciton polaritons and shows a pathway for realising new phases of quantum matter in a solid state.Comment: 7 pages, 4 figure