3,404 research outputs found
Photon heat transport in low-dimensional nanostructures
At low temperatures when the phonon modes are effectively frozen, photon
transport is the dominating mechanism of thermal relaxation in metallic
systems. Starting from a microscopic many-body Hamiltonian, we develop a
nonequilibrium Green's function method to study energy transport by photons in
nanostructures. A formally exact expression for the energy current between a
metallic island and a one-dimensional electromagnetic field is obtained. From
this expression we derive the quantized thermal conductance as well as show how
the results can be generalized to nonequilibrium situations. Generally, the
frequency-dependent current noise of the island electrons determines the energy
transfer rate.Comment: 4 pages, 3 Fig
Cyclostationary shot noise in mesoscopic measurements
We discuss theoretically a setup where a time-dependent current consisting of
a DC bias and two sinusoidal harmonics is driven through a sample. If the
sample exhibits current-dependent shot noise, the down-converted noise power
spectrum varies depending on the local-oscillator phase of the mixer. The
theory of this phase-dependent noise is applied to discuss the measurement of
the radio-frequency single-electron transistor. We also show that this effect
can be used to measure the shot noise accurately even in nonlinear
high-impedance samples.Comment: 3 pages, 2 figure
Quantum transitions induced by the third cumulant of current fluctuations
We investigate the transitions induced by external current fluctuations on a
small probe quantum system. The rates for the transitions between the energy
states are calculated using the real-time Keldysh formalism for the density
matrix evolution. We especially detail the effects of the third cumulant of
current fluctuations inductively coupled to a quantum bit and propose a setup
for detecting the frequency-dependent third cumulant through the transitions it
induces.Comment: 4 pages, 3 figure
Microwave response of an NS ring coupled to a superconducting resonator
A long phase coherent normal (N) wire between superconductors (S) is
characterized by a dense phase dependent Andreev spectrum . We probe this
spectrum in a high frequency phase biased configuration, by coupling an NS ring
to a multimode superconducting resonator. We detect a dc flux and frequency
dependent response whose dissipative and non dissipative components are related
by a simple Debye relaxation law with a characteristic time of the order of the
diffusion time through the N part of the ring. The flux dependence exhibits
periodic oscillations with a large harmonics content at temperatures
where the Josephson current is purely sinusoidal. This is explained considering
that the populations of the Andreev levels are frozen on the time-scale of the
experiments.Comment: 5 pages,4 figure
State-dependent impedance of a strongly coupled oscillator-qubit system
We investigate the measurements of two-state quantum systems (qubits) at
finite temperatures using a resonant harmonic oscillator as a quantum probe.
The reduced density matrix and oscillator correlators are calculated by a
scheme combining numerical methods with an analytical perturbation theory.
Correlators provide us information about the system impedance, which depends on
the qubit state. We show in detail how this property can be exploited in the
qubit measurement.Comment: 8 pages, 16 image
Self-Calibration of Cameras with Euclidean Image Plane in Case of Two Views and Known Relative Rotation Angle
The internal calibration of a pinhole camera is given by five parameters that
are combined into an upper-triangular calibration matrix. If the
skew parameter is zero and the aspect ratio is equal to one, then the camera is
said to have Euclidean image plane. In this paper, we propose a non-iterative
self-calibration algorithm for a camera with Euclidean image plane in case the
remaining three internal parameters --- the focal length and the principal
point coordinates --- are fixed but unknown. The algorithm requires a set of point correspondences in two views and also the measured relative
rotation angle between the views. We show that the problem generically has six
solutions (including complex ones).
The algorithm has been implemented and tested both on synthetic data and on
publicly available real dataset. The experiments demonstrate that the method is
correct, numerically stable and robust.Comment: 13 pages, 7 eps-figure
Effective capacitance in a single-electron transistor
Starting from the Kubo formula for conductance, we calculate the
frequency-dependent response of a single-electron transistor (SET) driven by an
ac signal. Treating tunneling processes within the lowest order approximation,
valid for a wide range of parameters, we discover a finite reactive part even
under Coulomb blockade due to virtual processes. At low frequencies this can be
described by an effective capacitance. This effect can be probed with microwave
reflection measurements in radio-frequency (rf) SET provided that the
capacitance of the surroundings does not completely mask that of the SET.Comment: 4 pages, 5 figures In the past few days we have noticed a serious
sign error in the theory presented in this preprint, which essentially
changes the sign of the capacitance correction. That is, otherwise the
physics is as described, but the sign is incorrect. The new version reflects
these change
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