1,465 research outputs found
Inelastic Interaction Corrections and Universal Relations for Full Counting Statistics
We analyze in detail the interaction correction to Full Counting Statistics
(FCS) of electron transfer in a quantum contact originating from the
electromagnetic environment surrounding the contact. The correction can be
presented as a sum of two terms, corresponding to elastic/inelastic electron
transfer. Here we primarily focus on the inelastic correction.
For our analysis, it is important to understand more general -- universal --
relations imposed on FCS only by quantum mechanics and statistics with no
regard for a concrete realization of a contact. So we derive and analyze these
relations. We reveal that for FCS the universal relations can be presented in a
form of detailed balance. We also present several useful formulas for the
cumulants.
To facilitate the experimental observation of the effect, we evaluate
cumulants of FCS at finite voltage and temperature. Several analytical results
obtained are supplemented by numerical calculations for the first three
cumulants at various transmission eigenvalues.Comment: 10 pages, 3 figure
Giant current fluctuations in an overheated single electron transistor
Interplay of cotunneling and single-electron tunneling in a thermally
isolated single-electron transistor (SET) leads to peculiar overheating
effects. In particular, there is an interesting crossover interval where the
competition between cotunneling and single-electron tunneling changes to the
dominance of the latter. In this interval, the current exhibits anomalous
sensitivity to the effective electron temperature of the transistor island and
its fluctuations. We present a detailed study of the current and temperature
fluctuations at this interesting point. The methods implemented allow for a
complete characterization of the distribution of the fluctuating quantities,
well beyond the Gaussian approximation. We reveal and explore the parameter
range where, for sufficiently small transistor islands, the current
fluctuations become gigantic. In this regime, the optimal value of the current,
its expectation value, and its standard deviation differ from each other by
parametrically large factors. This situation is unique for transport in
nanostructures and for electron transport in general. The origin of this
spectacular effect is the exponential sensitivity of the current to the
fluctuating effective temperature.Comment: 10 pages, 11 figure
Lamplighter model of a random copolymer adsorption on a line
We present a model of an AB-diblock random copolymer sequential
self-packaging with local quenched interactions on a one-dimensional infinite
sticky substrate. It is assumed that the A-A and B-B contacts are favorable,
while A-B are not. The position of a newly added monomer is selected in view of
the local contact energy minimization. The model demonstrates a
self-organization behavior with the nontrivial dependence of the total energy,
(the number of unfavorable contacts), on the number of chain monomers, :
for quenched random equally probable distribution of A- and
B-monomers along the chain. The model is treated by mapping it onto the
"lamplighter" random walk and the diffusion-controlled chemical reaction of
type with the subdiffusive motion of reagents.Comment: 8 pages, 5 figure
Effects of two dimensional plasmons on the tunneling density of states
We show that gapless plasmons lead to a universal
correction to the tunneling
density of states of a clean two dimensional Coulomb interacting electron gas.
We also discuss a counterpart of this effect in the "composite fermion metal"
which forms in the presence of a quantizing perpendicular magnetic field
corresponding to the half-filled Landau level. We argue that the latter
phenomenon might be relevant for deviations from a simple scaling observed by
A.Chang et al in the tunneling characteristics of Quantum Hall liquids.Comment: 12 pages, Latex, NORDITA repor
Superconducting Spin Qubits
We propose and theoretically investigate spin superconducting qubits. Spin
superconducting qubit consists of a single spin confined in a Josephson
junction. We show that owing to spin-orbit interaction, superconducting
difference across the junction can polarize this spin. We demonstrate that this
enables single qubit operations and more complicated quantum gates, where spins
of different qubits interact via a mutual inductance of superconducting loop
where the junctions are embedded. Recent experimental realizations of Josephson
junctions made of semiconductor quantum dots in contact with superconducting
leads have shown that the number of electrons in the quantum dot can be tuned
by a gate voltage. Spin superconducting qubit is realized when the number of
electrons is odd. We discuss the qubit properties at phenomenological level. We
present a microscopic theory that enables us to make accurate estimations of
the qubit parameters by evaluating the spin-dependent Josephson energy in the
framework of fourth-order perturbation theory.Comment: 11 pages, 8 figure
Hybrid superconducting quantum magnetometer
A superconducting quantum magnetometer based on magnetic flux-driven
modulation of the density of states of a proximized metallic nanowire is
theoretically analyzed. With optimized geometrical and material parameters
transfer functions up to a few mV/Phi_0 and intrinsic flux noise ~10^{-9}Phi_0
Hz^{-1/2} below 1 K are achievable. The opportunity to access single-spin
detection joined with limited dissipation (of the order of ~ 10^{-14} W) make
this magnetometer interesting for the investigation of the switching dynamics
of molecules or individual magnetic nanoparticles.Comment: 6 pages, 6 color figures, added calculation of the Josephson current,
published versio
Coherent and incoherent pumping of electrons in double quantum dots
We propose a new mode of operation of an electron pump consisting of two
weakly coupled quantum dots connected to reservoirs. An electron can be
transferred within the device at zero bias voltage when it is subjected to
electromagnetic radiation, thereby exciting the double dot. The excited state
can decay by transferring charge from one lead and to the other lead in one
direction. Depending on the energies of the intermediate states in the pumping
cycle, which are controlled by the gate voltages, this transport is either
incoherent via well-known sequential tunneling processes, or coherent via a
inelastic co-tunneling process. The latter novel mode of operation is possible
only when interdot Coulomb charging is important. The D.C. transport through
the system can be controlled by the frequency of the applied radiation. We
concentrate on the resonant case, when the frequency matches the energy
difference for exciting an electron from one dot into the other. The resonant
peaks in the pumping current should be experimentally observable. We have
developed a density matrix approach which describes the dynamics of the system
on timescales much larger than the period of the applied irradiation. In
contrast to previous works we additionally consider the case of slow modulation
of the irradiation amplitude. Harmonic modulation produces additional sidepeaks
in the photoresponse, and pulsed modulation can be used to resolve the Rabi
frequency in the time-averaged current.Comment: 5 pages, 6 figures. This is an extension of cond-mat/9707310 "A
coherent double-quantum-dot electron pump" This version has been accepted for
publication in Phys. Rev. B. Changes: Added references. Corrected typos.
Changed content mainly the introduction. Regime of device operation is now
specified more precisely. A stability diagram has been added as a figure has
been adde
Interplay of electromagnetic noise and Kondo effect in quantum dots
We investigate the influence of an electromagnetic environment, characterized
by a finite impedance , on the Kondo effect in quantum dots. The
circuit voltage fluctuations couple to charge fluctuations in the dot and
influence the spin exchange processes transferring charge between the
electrodes. We discuss how the low-energy properties of a Kondo quantum dot
subject to dynamical Coulomb blockade resemble those of Kondo impurities in
Luttinger liquids. Using previous knowledge based on the bosonization of
quantum impurity models, we show that low-voltage conductance anomalies appear
at zero temperature. The conductance can vanish at low temperatures even in
presence of a screened impurity spin. Moreover, the quantitative determination
of the corresponding Kondo temperature depends on the full frequency-dependent
impedance of the circuit. This is demonstrated by a weak-coupling calculation
in the Kondo interaction, taking into account the full distribution of
excited environmental modes.Comment: 10 pages, 4 figures, revised version, new titl
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