28 research outputs found
The new concept of nano-device spectroscopy based on Rabi-Bloch oscillations for THz-frequency range
We considered one-dimensional quantum chains of two-level Fermi particles
coupled via the tunneling driven both by ac and dc fields in the regimes of
strong and ultrastrong coupling. The frequency of ac field is matched with the
frequency of the quantum transition. Based on the fundamental principles of
electrodynamics and quantum theory, we developed a general model of quantum
dynamics for such interactions. We showed that the joint action of ac and dc
fields leads to the strong mutual influence of Rabi- and Bloch oscillations one
to another. We focused on the regime of ultrastrong coupling, for which Bloch-
and Rabi-frequencies are a significant values of the frequency of interband
transition. The Hamiltonian was solved numerically with account of
anti-resonant terms. It manifests by the appearance of great number of narrow
high-amplitude resonant lines in the spectra of tunneling current and dipole
moment. We proposed the new concept of THz spectroscopy promising for different
applications in future nanoelectronics and nano-photonics.Comment: 26 pages, 20 figure
Quantum antenna as an open system: strong antenna coupling with photonic reservoir
We proposed the general concept of quantum antenna in the strong coupling
regime. It is based on the theory of open quantum systems. The antenna emission
to the space is considered as an interaction with the thermal photonic
reservoir. For modeling of the antenna dynamics is formulated a master equation
with the correspondent Lindblad super-operators as the radiation terms. It is
shown that strong coupling dramatically changes the radiation pattern of
antenna. The total power pattern splits to three partial components; each
corresponds to the spectral line of Mollow triplet. We analyzed the dependence
of splitting from the length of antenna, shift of the phase, and
Rabi-frequency. The predicted effect opens a way for implementation of
multi-beam electrically tunable antennas, potentially useful in different
nano-devices
Discrete solitons in an array of quantum dots
We develop a theory for the interaction of classical light fields with an a
chain of coupled quantum dots (QDs), in the strong-coupling regime, taking into
account the local-field effects. The QD chain is modeled by a one-dimensional
(1D) periodic array of two-level quantum particles with tunnel coupling between
adjacent ones. The local-field effect is taken into regard as QD depolarization
in the Hartree-Fock-Bogoliubov approximation. The dynamics of the chain is
described by a system of two discrete nonlinear Schr\"{o}dinger (DNLS)
equations for local amplitudes of the probabilities of the ground and first
excited states. The two equations are coupled by a cross-phase-modulation cubic
terms, produced by the local-field action, and by linear terms too. In
comparison with previously studied DNLS systems, an essentially new feature is
a phase shift between the intersite-hopping constants in the two equations. By
means of numerical solutions, we demonstrate that, in this QD chain, Rabi
oscillations (RO) self-trap into stable bright\textit{\ Rabi solitons} or
\textit{Rabi breathers}. Mobility of the solitons is considered too. The
related behavior of observable quantities, such as energy, inversion, and
electric-current density, is given a physical interpretation. The results apply
to a realistic region of physical parameters.Comment: 12 pages, 10 figures, Phys. Rev. B, in pres
Scattering of the near field of an electric dipole by a single-wall carbon nanotube
The use of carbon nanotubes as optical probes for scanning near-field optical
microscopy requires an understanding of their near-field response. As a first
step in this direction, we investigated the lateral resolution of a carbon
nanotube tip with respect to an ideal electric dipole representing an
elementary detected object. A Fredholm integral equation of the first kind was
formulated for the surface electric current density induced on a single-wall
carbon nanotube (SWNT) by the electromagnetic field due to an arbitrarily
oriented electric dipole located outside the SWNT. The response of the SWNT to
the near field of a source electric dipole can be classified into two types,
because surface-wave propagation occurs with (i) low damping at frequencies
less than ~ 200-250 THz and (ii) high damping at higher frequencies. The
interaction between the source electric dipole and the SWNT depends critically
on their relative location and relative orientation, and shows evidence of the
geometrical resonances of the SWNT in the low-frequency regime. These
resonances disappear when the relaxation time of the SWNT is sufficiently low.
The far-field radiation intensity is much higher when the source electric
dipole is placed near an edge of SWNT than at the centroid of the SWNT. The use
of an SWNT tip in scattering-type scanning near-field optical microscopy can
deliver a resolution less than ~ 20 nm. Moreover, our study shows that the
relative orientation and distance between the SWNT and the nanoscale dipole
source can be detected.Comment: 23 pages, 16 figure
Politika prisustva: Kako onlajn aktivnosti uobličavaju oflajn aktivizam
The author explores how the internet and the new media are changing the way that we communicate, act and think, individually and collectively, through the example of the Occupy Wall Street Movement. The author claims that The Occupy Movement, as a post-narrative project conceived in a digital environment, is less of a political activity, and more a new way of behavior for its members and for the society at large. Its focus on consensus building and its modus operandi are reflecting the principles of the Internet, web-organization and cooperation. Therefore, its success is not about achieving any particular political aim, or winning an election, but about the general acceptance of these values and their becoming part of a wider political agenda.Autor istražuje kako internet i novi mediji menjaju način na koji komuniciramo, delujemo i mislimo, pojedinačno ali i kolektivno, na primeru pokreta „Okupirajmo Volstrit“. Autor tvrdi da „Okupacija Volstrita“, kao postnarativni pokret nastao u digitalnom okruženju, manje predstavlja političku aktivnost a više novi normativni način ponašanja za svoje članove, ali i čitavo društvo. Njegova usmerenost ka izgradnji konsenzusa, kao i sam modus funkcionisanja, odražavaju principe interneta, mrežne organizacije i kolaboracije. Zato je njegov uspeh manje povezan sa ostvarivanjem nekog pojedinačnog cilja ili osvajanja vlasti na izborima, a više sa razmerom u kojoj će ove rednosti biti opšteusvojene i postati deo ukupne političke agende
Bloch Oscillations in the Chains of Artificial Atoms Dressed with Photons
We present a model of one-dimensional chain of two-level artificial atoms driven with DC field and quantum light simultaneously in a strong coupling regime. The interaction of atoms with light leads to electron-photon entanglement (dressing of the atoms with light). The driving via dc field leads to the Bloch oscillations (BO) in the chain of dressed atoms. We consider the mutual influence of dressing and BO and show that scenario of oscillations dramatically differs from predicted by the Jaynes-Cummings and Bloch-Zener models. We study the evolution of the population inversion, tunneling current, photon probability distribution, mean number of photons, and photon number variance, and show the influence of BO on the quantum-statistical characteristics of light. For example, the collapse-revivals picture and vacuum Rabi-oscillations are strongly modulated with Bloch frequency. As a result, quantum properties of light and degree of electron-photon entanglement become controllable via adiabatic dc field turning. On the other hand, the low-frequency tunneling current depends on the quantum light statistics (in particular, for coherent initial state it is modulated accordingly the collapse-revivals picture). The developed model is universal with respect to the physical origin of artificial atom and frequency range of atom-light interaction. The model is adapted to the 2D-heterostructures (THz frequencies), semiconductor quantum dots (optical range), and Josephson junctions (microwaves). The data for numerical simulations are taken from recently published experiments. The obtained results open a new way in quantum state engineering and nano-photonic spectroscopy