175 research outputs found
Spontaneous decay of excited atomic states near a carbon nanotube
Spontaneous decay process of an excited atom placed inside or outside (near
the surface) a carbon nanotube is analyzed. Calculations have been performed
for various achiral nanotubes. The effect of the nanotube surface has been
demonstrated to dramatically increase the atomic spontaneous decay rate -- by 6
to 7 orders of magnitude compared with that of the same atom in vacuum. Such an
increase is associated with the nonradiative decay via surface excitations in
the nanotube.Comment: 8 pages, 3 figure
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
Spontaneous decay of an emitter's excited state near a finite-length metallic carbon nanotube
The spontaneous decay of an excited state of an emitter placed in the
vicinity of a metallic single-wall carbon nanotube (SWNT) was examined
theoretically. The emitter-SWNT coupling strongly depends on the position of
the emitter relative to the SWNT, the length of the SWNT, the dipole transition
frequency and the orientation of the emitter. In the high-frequency regime,
dips in the spectrum of the spontaneous decay rate exist at the resonance
frequencies in the spectrum of the SWNT conductivity. In the
intermediate-frequency regime, the SWNT conductivity is very low, and the
spontaneous decay rate is practically unaffected by the SWNT. In the
low-frequency regime, the spectrum of the spontaneous decay rate contains
resonances at the antennas resonance frequencies for surface-wave propagation
in the SWNT. Enhancement of both the total and radiative spontaneous decay
rates by several orders in magnitude is predicted at these resonance
frequencies. The strong emitter-field coupling is achieved, in spite of the low
Q factor of the antenna resonances, due to the very high magnitude of the
electromagnetic field in the near-field zone. The vacuum Rabi oscillations of
the population of the excited emitter state are exhibited when the emitter is
coupled to an antenna resonance of the SWNT.Comment: 8 pages, 6 figure
Microscopic theory of quantum dot interactions with quantum light: local field effect
A theory of both linear and nonlinear electromagnetic response of a single QD
exposed to quantum light, accounting the depolarization induced local--field
has been developed. Based on the microscopic Hamiltonian accounting for the
electron--hole exchange interaction, an effective two--body Hamiltonian has
been derived and expressed in terms of the incident electric field, with a
separate term describing the QD depolarization. The quantum equations of motion
have been formulated and solved with the Hamiltonian for various types of the
QD excitation, such as Fock qubit, coherent fields, vacuum state of
electromagnetic field and light with arbitrary photonic state distribution. For
a QD exposed to coherent light, we predict the appearance of two oscillatory
regimes in the Rabi effect separated by the bifurcation. In the first regime,
the standard collapse--revivals phenomenon do not reveal itself and the QD
population inversion is found to be negative, while in the second one, the
collapse--revivals picture is found to be strongly distorted as compared with
that predicted by the standard Jaynes-Cummings model. %The model developed can
easily be extended to %%electromagnetic excitation. For the case of QD
interaction with arbitrary quantum light state in the linear regime, it has
been shown that the local field induce a fine structure of the absorbtion
spectrum. Instead of a single line with frequency corresponding to which the
exciton transition frequency, a duplet is appeared with one component shifted
by the amount of the local field coupling parameter. It has been demonstrated
the strong light--mater coupling regime arises in the weak-field limit. A
physical interpretation of the predicted effects has been proposed.Comment: 14 pages, 7 figure
Anomalous electromagnetic coupling via entanglement at the nanoscale
This is the final version of the article. Available from IoP Publishing via the DOI in this record.Understanding unwanted mutual interactions between devices at the nanoscale is crucial for the study of the electromagnetic compatibility in nanoelectronic and nanophotonic systems. Anomalous electromagnetic coupling (crosstalk) between nanodevices may arise from the combination of electromagnetic interaction and quantum entanglement. In this paper we study in detail the crosstalk between two identical nanodevices, each consisting of a quantum emitter (atom, quantum dot, etc), capacitively coupled to a pair of nanoelectrodes. Using the generalized susceptibility concept, the overall system is modeled as a two-port within the framework of the electrical circuit theory and it is characterized by the admittance matrix. We show that the entanglement changes dramatically the physical picture of the electromagnetic crosstalk. In particular, the excitation produced in one of the ports may be redistributed in equal parts between both the ports, in spite of the rather small electromagnetic interactions. Such an anomalous crosstalk is expected to appear at optical frequencies in lateral GaAs double quantum dots. A possible experimental set up is also discussed. The classical concepts of interference in the operation of electronic devices, which have been known since the early days of radio-communications and are associated with electromagnetic compatibility, should then be reconsidered at the nanoscale.This research was supported in part by the EU Horizon 2020 project H2020-MSCA-RISE-2014-644076 CoExAN and EU FP7 projects, FP7-PEOPLE-2012-IRSES-316432 QOCaN and FP7-PEOPLE-2013-IRSES-612285 CANTOR. Discussions of the basic ideas underlying this work with Dr S Starobinets and Dr D Mogilevtsev are acknowledged
van der Waals coupling in atomically doped carbon nanotubes
We have investigated atom-nanotube van der Waals (vdW) coupling in atomically
doped carbon nanotubes (CNs). Our approach is based on the perturbation theory
for degenerated atomic levels, thus accounting for both weak and strong
atom-vacuum-field coupling. The vdW energy is described by an integral equation
represented in terms of the local photonic density of states (DOS). By solving
it numerically, we demonstrate the inapplicability of standard
weak-coupling-based vdW interaction models in a close vicinity of the CN
surface where the local photonic DOS effectively increases, giving rise to an
atom-field coupling enhancement. An inside encapsulation of atoms into the CN
has been shown to be energetically more favorable than their outside adsorption
by the CN surface. If the atom is fixed outside the CN, the modulus of the vdW
energy increases with the CN radius provided that the weak atom-field coupling
regime is realized (i.e., far enough from the CN). For inside atomic position,
the modulus of the vdW energy decreases with the CN radius, representing a
general effect of the effective interaction area reduction with lowering the CN
curvature.Comment: 15 pages, 5 figure
Quantum entanglement in electric circuits: From anomalous crosstalk to electromagnetic compatibility in nano-electronics
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record..We show that the electromagnetic coupling at the nanoscale may be accompanied by another coupling mechanism, related to quantum entanglement. Consequently, a combined 'electromagnetic-quantum' coupling is created, which stipulates long-distance and long-living interactions in electric circuits. Manifestation of this effect in electromagnetic compatibility (EMC) is discussed. An efficient theoretical framework for EMC analysis in nanoelectronics is developed based on the generalized theory of electric circuits. It is shown that the action of quantum entanglement is equivalent to an addition of the supplementary elements in electric circuit with the effective admittances defined as general susceptibilities that can be calculated using the Kubo-technique.This work was supported in part by EU grants FP7-PEOPLE-2009-IRSES-
247007 CACOMEL and FP7-PEOPLE-2013-IRSES- 612285 CANTOR
Spontaneous decay dynamics in atomically doped carbon nanotubes
We report a strictly non-exponential spontaneous decay dynamics of an excited
two-level atom placed inside or at different distances outside a carbon
nanotube (CN). This is the result of strong non-Markovian memory effects
arising from the rapid variation of the photonic density of states with
frequency near the CN. The system exhibits vacuum-field Rabi oscillations, a
principal signature of strong atom-vacuum-field coupling, when the atom is
close enough to the nanotube surface and the atomic transition frequency is in
the vicinity of the resonance of the photonic density of states. Caused by
decreasing the atom-field coupling strength, the non-exponential decay dynamics
gives place to the exponential one if the atom moves away from the CN surface.
Thus, atom-field coupling and the character of the spontaneous decay dynamics,
respectively, may be controlled by changing the distance between the atom and
CN surface by means of a proper preparation of atomically doped CNs. This opens
routes for new challenging nanophotonics applications of atomically doped CN
systems as various sources of coherent light emitted by dopant atoms.Comment: 10 pages, 4 figure
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