2,963 research outputs found
Semiclassical analysis of level widths for one-dimensional potentials
We present a semiclassical study of level widths for a class of
one-dimensional potentials in the presence of an ohmic environment. Employing
an expression for the dipole matrix element in terms of the Fourier transform
of the classical path we obtain the level widths within the Golden rule
approximation. It is found that for potentials with an asymptotic power-law
behavior, which may in addition be limited by an infinite wall, the width that
an eigenstate of the isolated system acquires due to the coupling to the
environment is proportional to its quantum number.Comment: 8 pages, 2 figures, RevTe
What do phase space methods tell us about disordered quantum systems?
Introduction
Phase space methods in quantum mechanics
- The Wigner function
- The Husimi function
- Inverse participation ratio
Anderson model in phase space
- Husimi functions
- Inverse participation ratiosComment: 14 pages, 4 figures. To be published in "The Anderson Transition and
its Ramifications - Localisation, Quantum Interference, and Interactions",
ed. by T. Brandes and S. Kettemann, Lecture Notes in Physics
(http://link.springer.de/series/lnpp/) (Springer Verlag,
Berlin-Heidelberg-New York
Coulomb blockade of non-local electron transport in metallic conductors
We consider a metallic wire coupled to two metallic electrodes via two
junctions placed nearby. A bias voltage applied to one of such junctions alters
the electron distribution function in the wire in the vicinity of another
junction thus modifying both its noise and the Coulomb blockade correction to
its conductance. We evaluate such interaction corrections to both local and
non-local conductances demonstrating non-trivial Coulomb anomalies in the
system under consideration. Experiments on non-local electron transport with
Coulomb effects can be conveniently used to test inelastic electron relaxation
in metallic conductors at low temperatures.Comment: Published version. 11 pages, 4 figures. New references added,
discussion and introduction are extended, appendices adde
Cascaded half-harmonic generation of femtosecond frequency combs in mid-IR
For the growing demand of frequency combs in mid-infrared (mid-IR), known as
the "molecular fingerprint" region of the spectrum [1], down conversion of
near-IR frequency combs through half- harmonic generation offers numerous
benefits including high conversion efficiency and intrinsic phase and frequency
locking to the near-IR pump [2]. Hence cascaded half-harmonic generation
promises a simple path towards extending the wavelength coverage of stable
frequency combs. Here, we report a two-octave down-conversion of a frequency
comb around 1 {\mu}m through cascaded half-harmonic generation with ~64%
efficiency in the first stage, and ~18% in the second stage. We obtain
broadband intrinsically-frequency-locked frequency combs with ~50-fs pulses at
~2 {\mu}m and ~110-fs pulses at ~4 {\mu}m. These results indicate the
effectiveness of half-harmonic generation as a universal tool for efficient
phase- and frequency-locked down-conversion, which can be beneficial for
numerous applications requiring long-wavelength coherent sources
Surface plasmon in metallic nanoparticles: renormalization effects due to electron-hole excitations
The electronic environment causes decoherence and dissipation of the
collective surface plasmon excitation in metallic nanoparticles. We show that
the coupling to the electronic environment influences the width and the
position of the surface plasmon resonance. A redshift with respect to the
classical Mie frequency appears in addition to the one caused by the spill-out
of the electronic density outside the nanoparticle. We characterize the
spill-out effect by means of a semiclassical expansion and obtain its
dependence on temperature and the size of the nanoparticle. We demonstrate that
both, the spill-out and the environment-induced shift are necessary to explain
the experimentally observed frequencies and confirm our findings by
time-dependent local density approximation calculations of the resonance
frequency. The size and temperature dependence of the environmental influence
results in a qualitative agreement with pump-probe spectroscopic measurements
of the differential light transmission.Comment: 15 pages, 8 figures; version accepted in PR
Coherent phonon dynamics at the martensitic phase transition of Ni_2MnGa
We use time-resolved optical reflectivity to study the laser stimulated
dynamics in the magnetic shape memory alloy Ni_2MnGa. We observe two coherent
optical phonons, at 1.2 THz in the martensite phase and at 0.7 THz in the
pre-martensite phase, which we interpret as a zone-folded acoustic phonon and a
heavily damped amplitudon respectively. In the martensite phase the martensitic
phase transition can be induced by a fs laser pulse on a timescale of a few ps.Comment: 3 figure
Low noise buffer amplifiers and buffered phase comparators for precise time and frequency measurement and distribution
Extremely low noise, high performance, wideband buffer amplifiers and buffered phase comparators were developed. These buffer amplifiers are designed to distribute reference frequencies from 30 KHz to 45 MHz from a hydrogen maser without degrading the hydrogen maser's performance. The buffered phase comparators are designed to intercompare the phase of state of the art hydrogen masers without adding any significant measurement system noise. These devices have a 27 femtosecond phase stability floor and are stable to better than one picosecond for long periods of time. Their temperature coefficient is less than one picosecond per degree C, and they have shown virtually no voltage coefficients
Tunneling Spectroscopy of Two-level Systems Inside Josephson Junction
We consider a two-level (TL) system with energy level separation Omega_0
inside a Josephson junction. The junction is shunted by a resistor R and is
current I (or voltage V = RI) biased. If the TL system modulates the Josephson
energy and/or is optically active, it is Rabi driven by the Josephson
oscillations in the running phase regime near the resonance 2eV = Omega_0. The
Rabi oscillations, in turn, translate into oscillations of current and voltage
which can be detected in noise measurements. This effect provides an option to
fully characterize the TL systems and to find the TL's contribution to the
decoherence when the junction is used as a qubit.Comment: 4 page
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