Nonlinear Dynamics of Parametric Oscillations of Exciton–Polaritons in a Semiconductor Microcavity

Journal of Experimental and Theoretical Physics - The polariton dynamics in a microcavity in the parametric oscillator mode is studied when two pump polaritons turn into polaritons of signal and...     

Nonlinear Dynamics of Parametric Oscillations of Exciton–Polaritons in a Semiconductor Microcavity with Allowance for Decay

Optics and Spectroscopy - We have studied the dynamics of polaritons in a microcavity in the parametric oscillator regime, when the pump is carried out by two laser pulses with close frequencies....     

Dynamics of a Spinor Exciton–Polariton System in Laterally Strained GaAs Microcavities under Resonant Photoexcitation

The evolution of the spatial coherence and the polarization has been studied in a freely decaying polariton condensate that is resonantly excited by linearly polarized picosecond laser pulses at the lower and upper sublevels of the lower polariton branch in a high-Q GaAs-based microcavity with a reduced lateral symmetry without excitation of the exciton reservoir. It is found that the condensate inherits the coherence of the exciting laser pulse at both sublevels in a wide range of excitation densities and retains it for several dozen picoseconds. The linear polarization of the photoexcited condensate is retained only in the condensate at the lower sublevel. The linearly polarized condensate excited at the upper sublevel loses its stability at the excitation densities higher a threshold value: it enters a regime of internal Josephson oscillations with strongly oscillating circular and diagonal linear degrees of polarization. The polariton–polariton interaction leads to the nonlinear Josephson effects at high condensate densities. All the effects are well described in terms of the spinor Gross–Pitaevskii equations. The cause of the polarization instability of the condensate is shown to be the spin anisotropy of the polariton–polariton interaction.     

From the N-body Schrödinger Equation to the Quantum Boltzmann Equation: a Term-by-Term Convergence Result in the Weak Coupling Regime

In this paper we analyze the asymptotic dynamics of a system of N quantum particles, in a weak coupling regime. Particles are assumed statistically independent at the initial time. Our approach follows the strategy introduced by the authors in a previous work [BCEP1]: we compute the time evolution of the Wigner transform of the one-particle reduced density matrix; it is represented by means of a perturbation series, whose expansion is obtained upon iterating the Duhamel formula; this approach allows us to follow the arguments developed by Lanford [L] for classical interacting particles evolving in a low density regime. We prove, under suitable assumptions on the interaction potential, that the complete perturbation series converges term-by-term, for all times, towards the solution of a Boltzmann equation. The present paper completes the previous work [BCEP1]: it is proved there that a subseries of the complete perturbation expansion converges uniformly, for short times, towards the solution to the nonlinear quantum Boltzmann equation. This previous result holds for (smooth) potentials having possibly non-zero mean value. The present text establishes that the terms neglected at once in [BCEP1], on a purely heuristic basis, indeed go term-by-term to zero along the weak coupling limit, at least for potentials having zero mean. Our analysis combines stationary phase arguments with considerations on the nature of the various Feynman graphs entering the expansion.     

Generalized Rashba Coupling Approximation to a Resonant Spin Hall Effect of the Spin–Orbit Coupling System in a Magnetic Field

We introduce a generalized Rashba coupling approximation to analytically solve confined two-dimensional electron systems with both the Rashba and Dresselhaus spin–orbit couplings in an external magnetic field. A solvable Hamiltonian is obtained by performing a simple change of basis, which has the same form as that with only Rashba coupling. Each Landau state becomes a new displaced-Fock state instead of the original Harmonic oscillator Fock state. Analytical energies are consistent with the numerical ones in a wide range of coupling strength even for a strong Zeeman splitting, exhibiting the validity of the analytical approximation. By using the eigenstates, spin polarization correctly displays a jump at the energy-level crossing point, where the corresponding spin conductance exhibits a pronounced resonant peak. As the component of the Dresselhaus coupling increases,the resonant point shifts to a smaller value of the magnetic field. In contrast to pure Rashba couplings, we find that the Dresselhaus coupling and Zeeman splittings tend to suppress the resonant spin Hall effect. Our method provides an easy-to-implement analytical treatment to two-dimensional electron gas systems with both types of spin–orbit couplings by applying a magnetic field.     

Role of the Near-Surface Region of a Substrate in a Two-Dimensional Phase Transition Leading to the Growth of Single-Layer Graphene: The Pt–C System

JETP Letters - A new approach to the growth and destruction of graphene owing to a two-dimensional first-order condensation phase transition on metals dissolving carbon has been proposed and...     

Ferromagnetic Resonance and the Dynamics of the Magnetic Moment in a “Josephson Junction—Nanomagnet” System

JETP Letters - The dynamics of a nanomagnet coupled to a Josephson junction has been studied. Although a magnetic field induced by the superconducting current in the Josephson junction is very...     

Energy Exchange Dynamics and Relaxation of Excitations upon Strong Exciton–Plasmon Interaction in a Planar Nanostructure of Molecular J-Aggregates on a Metal Substrate

The kinetics of energy exchange between the plasmonic and excitonic subsystems in a “metal–dielectric–molecular layer” is studied for a planar composite nanostructure with a strong exciton–plasmon interaction. It is shown that the time dependence of the energy transfer between the components of the system has the character of damped oscillations, which depend on the prepared initial state, a number of relaxation parameters, the Rabi frequency, and the detuning from resonance.     

Loss of Ergodicity in the Transition from Annealed to Quenched Disorder in a Finite Kinetic Ising Model

We consider a kinetic Ising model which represents a generic agent-based model for various types of socio-economic systems. We study the case of a finite (and not necessarily large) number of agents N as well as the asymptotic case when the number of agents tends to infinity. The main ingredient are individual decision thresholds which are either fixed over time (corresponding to quenched disorder in the Ising model, leading to nonlinear deterministic dynamics which are generically non-ergodic) or which may change randomly over time (corresponding to annealed disorder, leading to ergodic dynamics). We address the question how increasing the strength of annealed disorder relative to quenched disorder drives the system from non-ergodic behavior to ergodicity. Mathematically rigorous analysis provides an explicit and detailed picture for arbitrary realizations of the quenched initial thresholds, revealing an intriguing “jumpy” transition from non-ergodicity with many absorbing sets to ergodicity. For large N we find a critical strength of annealed randomness, above which the system becomes asymptotically ergodic. Our theoretical results suggests how to drive a system from an undesired socio-economic equilibrium (e.g. high level of corruption) to a desirable one (low level of corruption).     

“Magic Relation” Between the Structures of Coexisting Phases at a First-Order Phase Transition in a Hard Sphere System

In the statistical geometry of a hard sphere system of any number of dimensions, V _o and S _o, the so-called available space and the area of the interface between the available and unavailable space, respectively, can be used as surrogates for chemical potential and pressure. It is shown exactly that, if a first-order transition occurs, the relation dV _o/dS _o=–/2D, where is the diameter of a sphere and D is the dimensionality of the system, must hold for densities in the phase coexistence region. This relation is remarkable in that –/2D is the ratio of the volume to the surface area of a sphere. Also, it is shown that it is possible for the system to have two successive first-order transitions, but that the occurrence of a continuous transition (even in two dimensions) is unlikely. It is argued that this unlikelihood is substantially strengthened by the absence of temperature (except as a trivial factor) as a variable in hard-sphere systems. This suggests that the findings of the KTHNY theory, recent simulations, and colloid experiments (specialized to sticky hard disks) can be extended to true hard disks. The fundamental physics underlying the magic relation is yet to be exposed. The author continues to search for the underlying reason and hopes that the present paper will stimulate others to join the search.     

Output Intensity Variations of the Laser Used in a Prism Coupling System and Its Application

The output intensity variations of the laser used in a prism coupling system are observed and found to be induced by the external optical feedback, which comes from the reflection on the prism. The intensity variations are explained with laser theory. The trough in the intensity variation corresponds to the position of the prism when the output light beam propagates perpendicularly to the prism. Based on the trough a new method for rotating the prism and reading out the step numbers is proposed, by which the angle 0° in the system need not to be calibrated. It is proven by experiment that the new method would improve the accuracy of the refractive index up to ±0.00001 and thickness to ±1 nm.     

Rigorous Treatment of the Liquid-Vapor Transition in a Polydisperse System with Kac Interaction

Within the canonical formalism, we consider a polydisperse lattice-gas model and a polydisperse continuous system interacting with the Kac potential. We obtain rigorous expressions for free energy densities. We also exhibit phase diagrams of the bidisperse lattice-gas model.     

Erratum to: “Numerical simulation of the two-phase flow produced by spraying a liquid by a nozzle”

Technical Physics - Page 1010, left column, line 4 from bottom should read “radius RAPP” instead of “diameter DAPP” Page 1010, right column, before the formula (19) should...     

Erratum to: “Time-Harmonic Gaussian Beams: Exact Solutions of the Helmhotz Equation in Free Space”

Optics and Spectroscopy - Equation (25) should be read as follows: