3,174 research outputs found
Inducing odd-frequency triplet superconducting correlations in a normal metal
This work discusses theoretically the interplay between the superconducting
and ferromagnetic proximity effects, in a diffusive normal metal strip in
contact with a superconductor and a non-uniformly magnetized ferromagnetic
insulator. The quasiparticle density of states of the normal metal shows clear
qualitative signatures of triplet correlations with spin one (TCS1). When one
goes away from the superconduting contact, TCS1 focus at zero energy under the
form of a peak surrounded by dips, which show a typical spatial scaling
behavior. This behavior can coexist with a focusing of singlet correlations and
triplet correlations with spin zero at finite but subgap energies. The
simultaneous observation of both effects would enable an unambigous
characterization of TCS1.Comment: To appear in Physical Review Letter
Probing coherent Cooper pair splitting with cavity photons
This work discusses theoretically the behavior of a microwave cavity and a
Cooper pair beam splitter (CPS) coupled non-resonantly. The cavity frequency
pull is modified when the CPS is resonant with a microwave excitation. This
provides a direct way to probe the coherence of the Cooper pair splitting
process. More precisely, the cavity frequency pull displays an anticrossing
whose specificities can be attributed unambiguously to coherent Cooper pair
injection. This work illustrates that microwave cavities represent a powerful
tool to investigate current transport in complex nanocircuits.Comment: 7 pages, 4 figure
Conductance and current noise of a superconductor/ferromagnet quantum point contact
We study the conductance and current noise of a superconductor/ferromagnet
(S/F) single channel Quantum Point Contact (QPC) as a function of the QPC bias
voltage, using a scattering approach. We show that the Spin-Dependence of
Interfacial Phase Shifts (SDIPS) acquired by electrons upon scattering by the
QPC can strongly modify these signals. For a weakly transparent contact, the
SDIPS induces sub-gap resonances in the conductance and differential Fano
factor curves of the QPC. For high transparencies, these resonances are
smoothed, but the shape of the signals remain extremely sensitive to the SDIPS.
We show that noise measurements could help to gain more information on the
device, e.g. in cases where the SDIPS modifies qualitatively the differential
Fano factor of the QPC but not the conductance.Comment: 9 pages, 4 figure
A spin quantum bit with ferromagnetic contacts for circuit QED
We theoretically propose a scheme for a spin quantum bit based on a double
quantum dot contacted to ferromagnetic elements. Interface exchange effects
enable an all electric manipulation of the spin and a switchable strong
coupling to a superconducting coplanar waveguide cavity. Our setup does not
rely on any specific band structure and can in principle be realized with many
different types of nanoconductors. This allows to envision on-chip single spin
manipulation and read-out using cavity QED techniques
Divide and conquer in ABC: Expectation-Progagation algorithms for likelihood-free inference
ABC algorithms are notoriously expensive in computing time, as they require
simulating many complete artificial datasets from the model. We advocate in
this paper a "divide and conquer" approach to ABC, where we split the
likelihood into n factors, and combine in some way n "local" ABC approximations
of each factor. This has two advantages: (a) such an approach is typically much
faster than standard ABC and (b) it makes it possible to use local summary
statistics (i.e. summary statistics that depend only on the data-points that
correspond to a single factor), rather than global summary statistics (that
depend on the complete dataset). This greatly alleviates the bias introduced by
summary statistics, and even removes it entirely in situations where local
summary statistics are simply the identity function.
We focus on EP (Expectation-Propagation), a convenient and powerful way to
combine n local approximations into a global approximation. Compared to the EP-
ABC approach of Barthelm\'e and Chopin (2014), we present two variations, one
based on the parallel EP algorithm of Cseke and Heskes (2011), which has the
advantage of being implementable on a parallel architecture, and one version
which bridges the gap between standard EP and parallel EP. We illustrate our
approach with an expensive application of ABC, namely inference on spatial
extremes.Comment: To appear in the forthcoming Handbook of Approximate Bayesian
Computation (ABC), edited by S. Sisson, L. Fan, and M. Beaumon
Mesoscopic admittance of a double quantum dot
We calculate the mesoscopic admittance of a double quantum dot
(DQD),which can be measured directly using microwave techniques. This quantity
reveals spectroscopic information on the DQD and is also directly sensitive to
a Pauli spin blockade effect. We then discuss the problem of a DQD coupled to a
high quality photonic resonator. When the photon correlation functions can be
developed along a random-phase-approximation-like scheme, the response of the
resonator gives an access to
Squeezing light with Majorana fermions
Coupling a semiconducting nanowire to a microwave cavity provides a powerfull
means to assess the presence or absence of isolated Majorana fermions in the
nanowire. These exotic bound states can cause a significant cavity frequency
shift but also a strong cavity nonlinearity leading for instance to light
squeezing. The dependence of these effects on the nanowire gate voltages gives
direct signatures of the unique properties of Majorana fermions, such as their
self-adjoint character and their exponential confinement.Comment: long version: 11 pages, 5 figure
Subradiant split Cooper pairs
We suggest a way to characterize the coherence of the split Cooper pairs
emitted by a double-quantum-dot based Cooper pair splitter (CPS), by studying
the radiative response of such a CPS inside a microwave cavity. The coherence
of the split pairs manifests in a strongly nonmonotonic variation of the
emitted radiation as a function of the parameters controlling the coupling of
the CPS to the cavity. The idea to probe the coherence of the electronic states
using the tools of Cavity Quantum Electrodynamics could be generalized to many
other nanoscale circuits.Comment: Main text + Supplemental material file (15 pages, 5 figures), to
appear in Physical Review Letter
Numerical analysis of a penalization method for the three-dimensional motion of a rigid body in an incompressible viscous fluid
We present and analyze a penalization method wich extends the the method of
[1] to the case of a rigid body moving freely in an incompressible fluid. The
fluid-solid system is viewed as a single variable density flow with an
interface captured by a level set method. The solid velocity is computed by
averaging at avery time the flow velocity in the solid phase. This velocity is
used to penalize the flow velocity at the fluid-solid interface and to move the
interface. Numerical illustrations are provided to illustrate our convergence
result. A discussion of our result in the light of existing existence results
is also given. [1] Ph. Angot, C.-H. Bruneau and P. Fabrie, A penalization
method to take into account obstacles in incompressible viscous flows, Numer.
Math. 81: 497--520 (1999)Comment: 23 page
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