We consider the 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 L configuration, where an upper level is coupled to a twofold degenerate lower level. 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 the considered system which strictly exhibits nonclassical properties.
We investigated several proposals utilizing the unique electronic properties of carbon nanotubes (CNTs) for a broad range of applications to THz optoelectronics, including THz generation by Cerenkov-type emitters based on carbon nanotubes and by hot electrons in quasimetallic nanotubes, frequency multiplication in chiral-nanotube-based superlattices controlled by a transverse electric field, and THz radiation detection and emission by armchair nanotubes in a strong magnetic field. Dispersion equations of the electron beam instability and the threshold conditions of the stimulated emission have been derived and analyzed, demonstrating realizability of the nanotube-based nanoFEL at realistic parameters of nanotubes and electronic beams.
Basic equations of electrodynamics of carbon nanotubes (CNTs are formulated in the helical parametrization scheme, where the crystalline structure of non-zigzag (n_1,n_2) CNTs is described as a set of n_2 double helices, and the electron energy spectrum of the CNTs consists of n_2 different helicoidal branches. The parametrization scheme is shown to be natural and more convenient for analyzing the electromagnetic response properties of chiral CNTs. Bloch equations for the density matrix have been obtained and adapted for the helical parametrization that allows studying the interaction between chiral CNTs and electromagnetic fields with arbitrary polarization and spatial structure. Linear transverse conductivity of chiral CNTs has been derived and utilized for the formulation of the effective boundary conditions for electromagnetic field on the surface of a chiral CNT. As an example, the spectra of high-order harmonics in chiral CNTs have been evaluated from the Bloch equations.
The parametrization scheme for carbon nanotubes (CNTs), helical parametrization, has been developed,
where the crystalline structure of non-zigzag (n1, n2) CNTs is described as a set of n2 double helices, and the
electron energy spectrum of the CNTs consists of n2 different helicoidal branches. The parametrization scheme is
shown to be natural and more convenient for analyzing the electromagnetic response properties of chiral CNTs.
Bloch equations for the density matrix have been obtained and adapted for the helical parametrization that
allows studying the interaction between chiral CNTs and electromagnetic fields with arbitrary polarization and
spatial structure. As an example, the spectra of high-order harmonics in chiral CNTs have been evaluated from
the Bloch equations.
We formulate and justify several proposals utilizing the unique electronic properties of different types of carbon
nanotubes in a broad range of applications to THz optoelectronics, including THz generation by hot electrons in
quasi-metallic nanotubes, frequency multiplication in chiral-nanotube-based superlattices controlled by a transverse
electric field, and THz radiation detection by armchair nanotubes in strong magnetic fields.
Electron motion in an (n,1) carbon nanotube is shown to correspond to a de Broglie wave propagating along a helical line on the nanotube wall. This helical motion leads to periodicity of the electron potential energy in the presence of an electric field normal to the nanotube axis. The period of this potential is proportional to the nanotube radius and is greater than the interatomic distance in the nanotube. As a result, the behavior of an electron in an (n,1) nanotube subject to a transverse electric field is similar to that in a semiconductor superlattice. In particular, Bragg scattering of electrons from the long-range periodic potential results in the opening of gaps in the energy spectrum of the nanotube. Modification of the bandstructure is shown to be significant for experimentally
attainable electric fields, which raises the possibility of applying this effect to novel nanoelectronic devices.
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