2,832 research outputs found
Spatial effects of Fano resonance in local tunneling conductivity in vicinity of impurity on semiconductor surface
We present the results of local tunneling conductivity spatial distribution
detailed theoretical investigations in vicinity of impurity atom for a wide
range of applied bias voltage. We observed Fano resonance in tunneling
conductivity resulting from interference between resonant tunneling channel
through impurity energy level and direct tunneling channel between the
tunneling contact leads. We have found that interference between tunneling
channels strongly modifies form of tunneling conductivity measured by the
scanning tunneling microscopy/spectroscopy (STM/STS) depending on the distance
value from the impurity.Comment: 4 pages, 3 figure
A multi-photon Stokes-parameter invariant for entangled states
We consider the Minkowskian norm of the n-photon Stokes tensor, a scalar
invariant under the group realized by the transformations of stochastic local
quantum operations and classical communications (SLOCC). This invariant is
offered as a candidate entanglement measure for n-qubit states and discussed in
relation to measures of quantum state entanglement for certain important
classes of two-qubit and three-qubit systems. This invariant can be directly
estimated via a quantum network, obviating the need to perform laborious
quantum state tomography. We also show that this invariant directly captures
the extent of entanglement purification due to SLOCC filters.Comment: 9 pages, 0 figures, Accepted for publication in Physical Review
Unscreened Coulomb repulsion in the one dimensional electron gas
A tight binding model of electrons interacting via bare Coulomb repulsion is
numerically investigated by use of the Density Matrix Renormalization Group
method which we prove applicable also to very long range potentials. From the
analysis of the elementary excitations, of the spin and charge correlation
functions and of the momentum distribution, a picture consistent with the
formation of a one dimensional "Wigner crystal" emerges, in quantitative
agreement with a previous bosonization study. At finite doping, Umklapp
scattering is shown to be ineffective in the presence of long range forces.Comment: RevTex, 5 pages with 8 eps figures. To be published on Phys. Rev.
Raman, infrared and optical spectra of the spin-Peierls compound NaV_2O_5
We have measured polarized spectra of Raman scattering, infrared and optical
transmission of NaV_2O_5 single crystals above the temperature of the
spin-Peierls transition Tsp=35 K. Some of the far-infrared (FIR) phonon lines
are strongly asymmetric, due to the spin-phonon interaction. In addition to the
phonon lines, a broad band was observed in the c(aa)c Raman spectrum and in the
E||a FIR transmission spectrum. A possible origin of these bands is discussed.
The absorption band at 10000 cm-1 1.25 eV is attributed to vanadium d-d
electronic transitions while the absorption edge above 3 eV is supposed to
correspond to the onset of charge-transfer transitions.Comment: 7 figures, 8 page
Resonant-state expansion of the Green's function of open quantum systems
Our series of recent work on the transmission coefficient of open quantum
systems in one dimension will be reviewed. The transmission coefficient is
equivalent to the conductance of a quantum dot connected to leads of quantum
wires. We will show that the transmission coefficient is given by a sum over
all discrete eigenstates without a background integral. An apparent
"background" is in fact not a background but generated by tails of various
resonance peaks. By using the expression, we will show that the Fano asymmetry
of a resonance peak is caused by the interference between various discrete
eigenstates. In particular, an unstable resonance can strongly skew the peak of
a nearby resonance.Comment: 7 pages, 7 figures. Submitted to International Journal of Theoretical
Physics as an article in the Proceedings for PHHQP 2010
(http://www.math.zju.edu.cn/wjd/
Time-dependent density-functional and reduced density-matrix methods for few electrons: Exact versus adiabatic approximations
To address the impact of electron correlations in the linear and non-linear
response regimes of interacting many-electron systems exposed to time-dependent
external fields, we study one-dimensional (1D) systems where the interacting
problem is solved exactly by exploiting the mapping of the 1D -electron
problem onto an -dimensional single electron problem. We analyze the
performance of the recently derived 1D local density approximation as well as
the exact-exchange orbital functional for those systems. We show that the
interaction with an external resonant laser field shows Rabi oscillations which
are detuned due to the lack of memory in adiabatic approximations. To
investigate situations where static correlations play a role, we consider the
time-evolution of the natural occupation numbers associated to the reduced
one-body density matrix. Those studies shed light on the non-locality and
time-dependence of the exchange and correlation functionals in time-dependent
density and density-matrix functional theories.Comment: 19 pages, 13 figures, version as published apart from layou
Time Evolution of tunneling and decoherence: soluble model
Decoherence effects associated to the damping of a tunneling two-level system
are shown to dominate the tunneling probability at short times in strong
coupling regimes in the context of a soluble model. A general decomposition of
tunneling rates in dissipative and unitary parts is implemented. Master
equation treatments fail to describe the model system correctly when more than
a single relaxation time is involved
Theory of Electromagnetic Wave Transmission through Metallic Gratings of Subwavelength Slits
We present FDTD calculations for transmission of light and other
electromagnetic waves through periodic arrays of slits in a metallic slab. The
results show resonant, frequency dependent, transmittance peaks for
subwavelength widths of the slits which can be up to a factor of ten with
respect to those out of resonance. Although our conclusions agree with previous
work by Lezec and Thio as regards both the magnitude of the enhancement and the
lack of contribution of surface plasmon polaritons of the metal surface to this
effect, we derive an interpretation from a theory that deals with emerging
beam- Rayleigh anomalies of the grating, and with Fabry-Perot resonances of the
perforated slab considered as an effective medium.Comment: 12 pages 3 figure
Quantitative comparison between theoretical predictions and experimental results for the BCS-BEC crossover
Theoretical predictions for the BCS-BEC crossover of trapped Fermi atoms are
compared with recent experimental results for the density profiles of Li.
The calculations rest on a single theoretical approach that includes pairing
fluctuations beyond mean field. Excellent agreement with experimental results
is obtained. Theoretical predictions for the zero-temperature chemical
potential and gap at the unitarity limit are also found to compare extremely
well with Quantum Monte Carlo simulations and with recent experimental results.Comment: 4 pages, 3 eps figure
Enhanced second harmonic generation from resonant GaAs gratings
We study second harmonic generation in nonlinear, GaAs gratings. We find
large enhancement of conversion efficiency when the pump field excites the
guided mode resonances of the grating. Under these circumstances the spectrum
near the pump wavelength displays sharp resonances characterized by dramatic
enhancements of local fields and favorable conditions for second harmonic
generation, even in regimes of strong linear absorption at the harmonic
wavelength. In particular, in a GaAs grating pumped at 1064nm, we predict
second harmonic conversion efficiencies approximately five orders of magnitude
larger than conversion rates achievable in either bulk or etalon structures of
the same material.Comment: 8 page
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