arXiv subjects

G. F. Mkrtchian

Publications and source records attributed to G. F. Mkrtchian.

At least 37 records · Page 2Linked to original sources

arXiv2017

Collective two-boson decay of excitons in Bose-Einstein condensate and generation of coherent photon-phonon radiation

The collective decay of excitons from initial Bose-Einstein condensate state is investigated theoretically. As practically more interesting case we consider excitons of the yellow series in the semiconductor cuprous oxide where we have collective photon and phonon assisted decay of excitons. It is shown that because of intrinsic instability of recoilless two-boson decay of Bose-Einstein condensate, the spontaneously emitted bosonic pairs are amplified leading to an exponential buildup of a macroscopic population into the certain modes. The collective decay rate has a nonlinear dependence on the excitonic density being comparable or larger than Auger recombination loss rate up to the high densities, which makes obtainable its observation. The considering phenomenon can also be applied for the realization of phonon laser.

cond-mat.mes-hall↗

arXiv2016

Coherent nonlinear optical response of graphene in the quantum Hall regime

We study nonlinear optical response of graphene in the quantum Hall regime to an intense laser pulse. In particular, we consider harmonic generation process. We demonstrate that the generalized magneto-optical conductivity of graphene on the harmonics of a strong pump laser radiation has a characteristic Hall plateaus feature. The plateaus heights depend on the laser intensity and broadening of Landau levels, so that are not quantized exactly. This nonlinear effect remains robust against the significant broadening of Landau levels. We predict realization of an experiment through the observation of the third harmonic signal and nonlinear Faraday effect, which are within the experimental feasibility.

cond-mat.mes-hall↗

arXiv2016

High harmonic generation in Landau-quantized graphene subjected to a strong electromagnetic radiation

We study nonlinear optical response of Landau quantized graphene to an intense electromagnetic wave. In particular, we consider high harmonic generation process. It is shown that one can achieve efficient generation of high harmonics with strong radiation fields -- when the work of the wave electric field on the magnetic length is larger than pump photon energy. At that high harmonics generation process takes place for a wide range of the pump wave frequencies and intensities even for significant broadening of Landau levels because of impurities in graphene.

cond-mat.mes-hall↗

arXiv2016

Enhanced harmonic generation and wave-mixing via two-color multiphoton excitation of atoms/molecules

We consider harmonics generation and wave-mixing by two-color multi photon resonant excitation of three-level atoms/molecules in strong laser fields. The coherent part of the spectra corresponding to multicolor harmonics generation is investigated. The obtained analytical results on the basis of generalized rotating wave approximation are in a good agreement with numerical calculations. The results applied to the hydrogen atom and homonuclear diatomic molecular ion show that one can achieve efficient generation of moderately high multicolor harmonics via multiphoton resonant excitation by appropriate laser pulses.

physics.atom-ph↗

arXiv2016

Nonlinear response of the quantum Hall system to a strong electromagnetic radiation

We study nonlinear response of a quantum Hall system in semiconductor-heterostructures via third harmonic generation process and nonlinear Faraday effect. We demonstrate that Faraday rotation angle and third harmonic radiation intensity have a characteristic Hall plateaus feature. These nonlinear effects remain robust against the significant broadening of Landau levels. We predict realization of an experiment through the observation of the third harmonic signal and Faraday rotation angle, which are within the experimental feasibility.

cond-mat.mes-hall↗

arXiv2015

Ultrarelativistic electron bunches of solid densities and nuclear radiation from nanolayers-plasma-targets under superintense laser pulses

We consider nonlinear interaction of superpower laser pulses of relativistic intensities with nanolayers and solid-plasma-targets towards the production of high energy-density electron bunches along with nuclear radiation (hard $% γ$-quanta and positron fluxes). It is shown that petawatt lasers are capable of producing via two-target scheme high density field free electron/positron bunches and substantial amounts of $γ$-quanta with energies up to $200$ MeV. For actual supershort and tightly focused--strongly nonplane ultrarelativistic laser pulses of linear and circular polarizations 3D3V problem is solved via numerical simulations.

physics.plasm-ph↗

arXiv2015

Nonlinear absorption of high-intensity shortwave radiation in plasma within relativistic quantum theory

On the base of the quantum kinetic equation for density matrix in plasma at the stimulated bremsstrahlung of electrons on ions, the nonlinear absorption rate for high-intensity shortwave radiation in plasma has been obtained within relativistic quantum theory. Both classical Maxwellian and degenerate quantum plasma are considered for x-ray lasers of high intensities. Essentially different dependences of nonlinear absorption rate on polarization of strong laser radiation is stated.

physics.plasm-ph↗

arXiv2014

Multiphoton interaction of a qutrit with single-mode quantized field in the ultrastrong and deep strong coupling regimes

We consider multiphoton dynamics of a quantum system composed of a three-state atom (a qutrit) and a single-mode photonic field in the ultrastrong and deep strong coupling regimes, when the coupling strength is comparable to or larger than the oscillator energy scale. We assume a qutrit to be in a polar-$Λ$ configuration in which two lower levels have mean dipole moments. Direct multiphoton resonant transitions revealing generalized Rabi oscillations, collapse, and revivals in atomic excitation probabilities for the ultrastrong couplings are studied. In the deep strong coupling regime particular emphasis is placed on the ground state of considering system which exhibits strictly nonclassical properties.

quant-ph↗

arXiv2013

Two-level system with broken inversion symmetry coupled to a quantum harmonic oscillator

We study the generalized Jaynes-Cummings model of quantum optics at the inversion-symmetry-breaking and in the ultrastrong coupling regime. With the help of a generalized multiphoton rotating-wave approximation, we study the stationary solutions of the Schrödinger equation. It is shown that the problem is reduced to resonant interaction of two position-displaced harmonic oscillators. Explicit expressions for the eigenstates and eigenvalues of generalized Jaynes-Cummings Hamiltonian are presented. We exemplify our physical model with analytical and numerical considerations regarding collapse and revivals of the initial population of a two-level system and photon distribution function at the direct multiphoton resonant coupling.

quant-ph↗

arXiv2013

Nonlinear absorption of ultrapower laser radiation by relativistic underdense plasma

The nonlinear absorption of laser radiation of relativistic intensities in the underdense plasma by a mechanism of stimulated bremsstrahlung of electrons on the ions/nuclei is investigated in the low frequency approximation. Coefficient of nonlinear inverse-bremsstrahlung absorption is studied for relativistic Maxwellian plasma at asymptotically large values of laser fields and high temperatures of electrons.

physics.atom-ph↗

arXiv2011

Creation of particle-hole superposition states in graphene at multiphoton resonant excitation by laser radiation

Nonlinear dynamics of establishment of electron-hole coherent superpositions states in graphene by multiphoton resonant excitation of interband transitions in laser fields is considered. The single-particle time dependent density matrix for such a quantized system is calculated in the multiphoton resonant approximation. The dependence of Rabi oscillations of Fermi-Dirac sea in graphene on the time, momentum, and photon number at multiphoton laser-excitation is analyzed.

cond-mat.mes-hall↗

arXiv2011

Relativistic quantum theory of high harmonic generation on atoms/ions by strong laser fields

High-order harmonic generation (HHG) by hydrogenlike atoms/ions in the uniform periodic electric field, formed by the two linearly polarized counterpropagating laser beams of relativistic intensities, is studied. The relativistic quantum theory of HHG in such fields, at which the impeding factor of relativistic magnetic drift of a strong wave can be eliminated, is presented arising from the Dirac equation. Specifically, a scheme of HHG in underdense plasma with the copropagating ultraintense laser and fast ion beams is proposed.

physics.atom-ph↗

arXiv2011

Quasimonoenergetic and low emittance ion bunch generation from ultrathin targets by counterpropagating laser pulses of ultrarelativistic intensities

A new method for generation of quasimonoenergetic and low emittance fast ion/nuclei bunches of solid densities from nanotargets by two counterpropagating laser pulses of ultrarelativistic intensities is proposed, based on the threshold phenomenon of particles "reflection" due to induced nonlinear Compton scattering. Particularly, a setup is considered which provides generation of ion bunches with parameters that are required in hadron therapy.

physics.plasm-ph↗

arXiv2011

Harmonics generation and intense terahertz radiation from polar molecules at multiphoton resonant excitation in laser fields

The coherent radiation spectrum of two-level polar molecules with UV transition is studied at the multiphoton resonant excitation by a moderately strong laser field. The spectrum corresponding to harmonic generation and low-frequency radiation is investigated both analytically and numerically. Specifically, a mechanism for generation of intense smoothly tunable terahertz radiation by two-level molecular configurations (with dynamic Stark shifts) possessing permanent dipole moments, is considered.

physics.atom-ph↗

arXiv2008

Universal quantum logic gates in a scalable Ising spin quantum computer

We consider the model of quantum computer, which is represented as a Ising spin lattice, where qubits (spin-half systems) are separated by the isolators (two spin-half systems). In the idle mode or at the single bit operations the total spin of isolators is 0. There are no need of complicated protocols for correcting the phase and probability errors due to permanent interaction between the qubits. We present protocols for implementation of universal quantum gates with the rectangular radio-frequency pulses.

quant-ph↗

arXiv2004

Quantum Theory of Generation of Coherent X-Ray in a Wiggler

In this paper we present the nonlinear quantum theory of X-Ray FEL in a wiggler. We present the solution of the Dirac equation in a space periodic strong magnetic field, which describes the quantum dynamics of a single electron in a wiggler. With the help of obtained wave function of an electron the self-consistent set of the Maxwell and relativistic quantum kinetic equations is obtained. Then, the process of coherent X-ray radiation generation in nonlinear quantum regime, when the photon energy is larger than resonance widths due to energetic/angular spreads of an electron beam and resonance width caused by finite interaction length, is investigated.

physics.acc-ph↗

arXiv2001

Non Linear Compton Scattering of Strong Laser Radiation on Channeled Particles in a Crystal

A version for intense $γ$-ray radiation based on the multiphoton scattering of strong laser radiation on relativistic particle beam channeled in a crystal is proposed. The scheme is considered when the incident laser beam and charged paricles beam are counter-propagating and the laser radiation is resonant to the energy levels of transversal motion of channeled particles.

quant-ph↗

arXiv2001

Relativistic Quantum Theory of Cyclotron Resonance in a Medium

In this paper the relativistic quantum theory of cyclotron resonance in an arbitrary medium is presented. The quantum equation of motion for charged particle in the field of plane electromagnetic wave and uniform magnetic field in a medium is solved in the eikonal approximation. The probabilities of induced multiphoton transitions between Landau levels in strong laser field is calculated.

quant-ph↗