2,760 research outputs found
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
Fully Overheated Single-Electron Transistor
We consider the fully overheated single-electron transistor, where the heat
balance is determined entirely by electron transfers. We find three distinct
transport regimes corresponding to cotunneling, single-electron tunneling, and
a competition between the two. We find an anomalous sensitivity to temperature
fluctuations at the crossover between the two latter regimes that manifests in
an exceptionally large Fano factor of current noise.Comment: 6 pages, 3 figures, includes Appendi
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
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
Suppression of Conductance in a Topological Insulator Nanostep Junction
We investigate quantum transport via surface states in a nanostep junction on
the surface of a 3D topological insulator that involves two different side
surfaces. We calculate the conductance across the junction within the
scattering matrix formalism and find that as the bias voltage is increased, the
conductance of the nanostep junction is suppressed by a universal factor of 1/3
compared to the conductance of a similar planar junction based on a single
surface of a topological insulator. We also calculate and analyze the Fano
factor of the nanostep junction and predict that the Fano factor saturates at
1/5, five times smaller than for a Poisson process
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