3,108 research outputs found
Semiclassical theory of current correlations in chaotic dot-superconductor systems
We present a semiclassical theory of current correlations in multiterminal
chaotic dot-superconductor junctions, valid in the absence of the proximity
effect in the dot. For a dominating coupling of the dot to the normal terminals
and a nonperfect dot-superconductor interface, positive cross correlations are
found between currents in the normal terminals. This demonstrates that positive
cross correlations can be described within a semiclassical approach. We show
that the semiclassical approach is equivalent to a quantum mechanical Green's
function approach with suppressed proximity effect in the dot.Comment: 5 pages, 3 figure
Multiple Andreev reflections in hybrid multiterminal junctions
We investigate theoretically charge transport in hybrid multiterminal
junctions with superconducting leads kept at different voltages. It is found
that multiple Andreev reflections involving several superconducting leads give
rise to rich subharmonic gap structures in the current-voltage characteristics.
The structures are evidenced numerically in junctions in the incoherent regime.Comment: 5 pages, 3 figure
Chaotic dot-superconductor analog of the Hanbury Brown Twiss effect
As an electrical analog of the optical Hanbury Brown Twiss effect, we study
current cross-correlations in a chaotic quantum dot-superconductor junction.
One superconducting and two normal reservoirs are connected via point contacts
to a chaotic quantum dot. For a wide range of contact widths and
transparencies, we find large positive current correlations. The positive
correlations are generally enhanced by normal backscattering in the contacts.
Moreover, for normal backscattering in the contacts, the positive correlations
survive when suppressing the proximity effect in the dot with a weak magnetic
field.Comment: 4 pages, 3 figure
Quantized dynamics of a coherent capacitor
A quantum coherent capacitor subject to large amplitude pulse cycles can be
made to emit or reabsorb an electron in each half cycle. Quantized currents
with pulse cycles in the GHz range have been demonstrated experimentally. We
develop a non-linear dynamical scattering theory for arbitrary pulses to
describe the properties of this very fast single electron source. Using our
theory we analyze the accuracy of the current quantization and investigate the
noise of such a source. Our results are important for future scientific and
possible metrological applications of this source.Comment: 4 pages, 2 figure
Orbital entanglement and violation of Bell inequalities in the presence of dephasing
We discuss orbital entanglement in mesoscopic conductors, focusing on the
effect of dephasing. The entanglement is detected via violation of a Bell
Inequality formulated in terms of zero-frequency current correlations.
Following closely the recent work by Samuelsson, Sukhorukov and Buttiker, we
investigate how the dephasing affects the possibility to violate the Bell
Inequality and how system parameters can be adjusted for optimal violation.Comment: 9 pages, 2 figures. To appear in a special issue on "Quantum
Computation at the Atomic Scale" in Turkish Journal of Physic
Quantum heat fluctuations of single particle sources
Optimal single electron sources emit regular streams of particles, displaying
no low frequency charge current noise. Due to the wavepacket nature of the
emitted particles, the energy is however fluctuating, giving rise to heat
current noise. We investigate theoretically this quantum source of heat noise
for an emitter coupled to an electronic probe in the hot-electron regime. The
distribution of temperature and potential fluctuations induced in the probe is
shown to provide direct information on the single particle wavefunction
properties and display strong non-classical features.Comment: 5 pages, 2 figure
Shot noise of photon-excited electron-hole pairs in open quantum dots
We investigate shot noise of photon-excited electron-hole pairs in open
multi-terminal, multi-channel chaotic dots. Coulomb interactions in the dot are
treated self-consistently giving a gauge-invariant expression for the finite
frequency correlations. The Coulomb interactions decrease the noise, the strong
interaction limit coincides with the non-interacting adiabatic limit. Inelastic
scattering and dephasing in the dot are described by voltage and dephasing
probe models respectively. We find that dephasing leaves the noise invariant,
but inelastic scattering decreases correlations eventually down to zero.Comment: 4 pages, 1 figure; minor changes, 3 references adde
Hanbury Brown Twiss effects in channel mixing normal-superconducting systems
An investigation of the role of the proximity effect in current cross
correlations in multiterminal, channel-mixing, normal-superconducting systems
is presented. The proposed experiment is an electrical analog of the optical
Hanbury Brown Twiss intensity cross correlation experiment. A chaotic quantum
dot is connected via quantum point contacts to two normal and one
superconducting reservoir. For dominating coupling of the dot to the
superconducting reservoir, a magnetic flux of the order of a flux quantum in
the dot suppresses the proximity effect and reverses the sign of the cross
correlations, from positive to negative. In the opposite limit, for a
dominating coupling to the normal reservoirs, the proximity effect is weak and
the cross correlation are positive for a nonideal contact between the dot and
the superconducting reservoir. We show that in this limit the correlations can
be explained with particle counting arguments.Comment: Invited talk at LT2
Entanglement in Anderson Nanoclusters
We investigate the two-particle spin entanglement in magnetic nanoclusters
described by the periodic Anderson model. An entanglement phase diagram is
obtained, providing a novel perspective on a central property of magnetic
nanoclusters, namely the temperature dependent competition between local Kondo
screening and nonlocal Ruderman-Kittel-Kasuya-Yoshida spin ordering. We find
that multiparticle entangled states are present for finite magnetic field as
well as in the mixed valence regime and away from half filling. Our results
emphasize the role of charge fluctuations.Comment: 5 pages, 3 figure
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