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.Comment: 12 pages, 1 figur

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-$\Lambda$ 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.Comment: 10 pages, 12 figures, Submitted to Phys. Rev.

High laser harmonics induced by the Berry curvature in time-reversal invariant materials

A new nonlinear scheme of high harmonics generation in a wide class of time-reversal invariant materials with broken spatial inversion symmetry (where recently the nonlinear Hall effect has been established) due to the nontrivial topology of bands is proposed. A microscopic quasiclassical theory describing the nonperturbative optical response of pseudo-relativistic electrons with nonzero Berry curvature of bands to a strong laser field is developed. We analyze the harmonic content of the induced current and show that one can decouple induced laser harmonics solely by the Berry curvature of bands. We also study the dependence of the nonlinear response on the driving wave and system parameters.Comment: 8 pages, 5 figure

High-order harmonic generation in gapped bilayer graphene

Microscopic nonlinear quantum theory of interaction of coherent electromagnetic radiation with gapped bilayer graphene is developed. The Liouville-von Neumann equation for the density matrix is solved numerically at the multiphoton excitation regime. The developed theory of interaction of charged carriers with strong driving wave field is valid near the Dirac points of the Brillouin zone. We consider the harmonic generation process in the nonadiabatic regime of interaction when the Keldysh parameter is of the order of unity. On the basis of numerical solutions, we examine the rates of odd and even high-harmonics at the particle-hole annihilation in the field of a strong pump wave of arbitrary polarization. Obtained results show that the gapped bilayer graphene can serve as an effective medium for generation of even and odd high harmonics in the THz and far infrared domains of frequencies.Comment: 15 pages, 9 figure

Multiphoton excitation and high-harmonics generation in topological insulator

Multiphoton interaction of coherent electromagnetic radiation with 2D metallic carriers confined on the surface of the 3D topological insulator is considered. A microscopic theory describing the nonlinear interaction of a strong wave and metallic carriers with many-body Coulomb interaction is developed. The set of integrodifferential equations for the interband polarization and carrier occupation distribution is solved numerically. Multiphoton excitation of Fermi-Dirac sea of 2D massless carriers is considered for a THz pump wave. It is shown that in the moderately strong pump wave field along with multiphoton interband/intraband transitions the intense radiation of high harmonics takes place.Comment: 13 pages, 7 figure

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 Schr\"{o}dinger 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.Comment: 5 pages, 5 figure

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.Comment: 4 pages, RevTe

Relativistic theory of the above-threshold multiphoton ionization of hydrogen-like atoms in the ultrastrong laser fields

The relativistic theory of above-threshold ionization (ATI) of hydrogen-like atoms in ultrastrong radiation fields, taking into account the photoelectron induced rescattering in the continuum spectrum is developed. It is shown that the contribution of the latter in the multiphoton ionization probability even in the Born approximation by Coulomb field is of the order of ATI probability in the scope of Keldysh-Faisal-Reiss ansatz.Comment: REVTeX, 13 page

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.Comment: 11 pages, RevTe

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 $\gamma$-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 $\gamma$-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.Comment: 6 pages, 6 figure