225 research outputs found
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- 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
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 -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 -quanta with
energies up to 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
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
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