846 research outputs found
Current fluctuations in composite conductors: Beyond the second cumulant
Employing the non-linear -model we analyze current fluctuations in
coherent composite conductors which contain a diffusive element in-between two
tunnel barriers. For such systems we explicitly evaluate the
frequency-dependent third current cumulant which also determines the leading
Coulomb interaction correction to shot noise. Our predictions can be directly
tested in future experiments.Comment: 6 pages, 1 figur
Full counting statistics of a general quantum mechanical variable
We present here a quantum mechanical framework for defining the statistics of
measurements of time integrals of A(t), A(t) being a quantum mechanical
variable. This is a generalization of the so-called full counting statistics
proposed earlier for DC electric currents.
We develop an influence functional formalism that allows us to study the
quantum system along with the measuring device thus fully accounting for the
action of the detector on the system to be measured. We define the full
counting statistics of an arbitrary variable by means of an evolution operator
that relates initial and final density matrices of the measuring device.
In this way we are able to resolve inconsistencies that occur in earlier
definitions. We suggest two schemes whereby the so defined full statistics can
be observed experimentally.Comment: 11 page
Full Counting Statistics of Cooper Pair Shuttling
The Cooper pair shuttle is a simple model system that combines features of
coherent and incoherent transport. We evaluate the full counting statistics
(FCS) of charge transfer via the shuttle in the incoherent regime. We describe
two limiting cases when the FCS allows for classical interpretation. Generally,
the classical interpretation fails yielding negative and imaginary
"probabilities". This signals that superconducting coherence survives even in
incoherent regime. We evaluate the current noise in some detail.Comment: 4 pages, 3 figures; v2 (published version) corrected misprint
Optical stabilization of voltage fluctuations in half-Josephson lasers
A recently proposed device, dubbed half-Josephson laser, provides a
phase-lock between the optical phase and the superconducting phase difference
between the leads of the device. In this paper we propose to utilize this
phase-lock for stabilization of voltage fluctuations, by two optical feedback
schemes. The first scheme involves a single half-Josephson laser and allows to
significantly decrease the diffusion coefficient of the superconducting phase
difference. The second scheme involves a stable optical source and a
fluctuating half-Josephson laser and permits quenching of the diffusion of the
relative phase of the lasers. This opens up perspectives of the optical control
of the superconducting phase and voltage fluctuations.Comment: 6 pages, 3 figure
Coulomb Blockade due to Quantum Phase-Slips Illustrated with Devices
In order to illustrate the emergence of Coulomb blockade from coherent
quantum phase-slip processes in thin superconducting wires, we propose and
theoretically investigate two elementary setups, or "devices". The setups are
derived from Cooper-pair box and Cooper-pair transistor, so we refer to them as
QPS-box and QPS-transistor, respectively. We demonstrate that the devices
exhibit sensitivity to a charge induced by a gate electrode, this being the
main signature of Coulomb blockade. Experimental realization of these devices
will unambiguously prove the Coulomb blockade as an effect of coherence of
phase-slip processes. We analyze the emergence of discrete charging in the
limit strong phase-slips. We have found and investigated six distinct regimes
that are realized depending on the relation between three characteristic energy
scales: inductive and charging energy, and phase-slip amplitude. For
completeness, we include a brief discussion of dual Josephson-junction devices
Full Current Statistics in the Regime of Weak Coulomb Interaction
We evaluate the full statistics of the current via a Coulomb island that is
strongly coupled to the leads. This strong coupling weakens Coulomb
interaction. We show that in this case the effects of the interaction can be
incorporated into the renormalization of transmission eigenvalues of the
scatterers that connect the island and the leads. We evaluate the Coulomb
blockade gap in the current-voltage characteristics, the value of the gap being
exponentially suppressed as compared to the classical charging energy of the
island.Comment: 4 pages, 3 figure
- …