856 research outputs found
Stabilized parametric Cooper-pair pumping in a linear array of coupled Josephson junctions
We present an experimentally realizable stabilized charge pumping scheme in a
linear array of Cooper-pair boxes. The system design intrinsically protects the
pumping mechanism from severe errors, especially current reversal and
spontaneous charge excitation. The quantum Zeno effect is implemented to
further diminish pumping errors. The characteristics of this scheme are
considered from the perspective of improving the current standard. Such an
improvement bears relevence to the closure of the so-called measurement
triangle (see D. Averin [Nature 434, 285 (2005)]).Comment: Title changed, other corrections and modifications requested from
Phys. Rev. Let
Accuracy of a mechanical single electron shuttle
Motivated by recent experiments, we calculate both the average current and
the current fluctuations for a metallic island which oscillates between two
symmetric electrodes. Electrons can only tunnel on or off the island when it is
close to one of the electrodes. Using a Master equation we investigate the
accuracy of such an electron shuttle both analytically and numerically. It is
shown that optimum operation is reached when the contact time is much larger
than the RC-time.Comment: RevTeX, 8 pages, 5 figure
Nonadiabatic Electron Pumping: Maximal Current with Minimal Noise
The noise properties of pump currents through an open double quantum dot
setup with non-adiabatic ac driving are investigated. Driving frequencies close
to the internal resonances of the double dot-system mark the optimal working
points at which the pump current assumes a maximum while its noise power
possesses a remarkably low minimum. A rotating-wave approximation provides
analytical expressions for the current and its noise power and allows to
optimize the noise characteristics. The analytical results are compared to
numerical results from a Floquet transport theory.Comment: 4 pages, 3 figures, replaced Fig. 1, added new inset in Fig. 2,
extended paragraph on symmetry consideration
Influence of Magnetic Field on Effective Electron-Electron Interactions in a Copper Wire
We have measured in a copper wire the energy exchange rate between
quasiparticles as a function of the applied magnetic field. We find that the
effective electron-electron interaction is strongly modified by the magnetic
field, suggesting that magnetic impurities play a role on the interaction
processes.Comment: latex anthore.tex, 8 files, 6 figures, 7 pages in: Proceedings of the
XXXVIth Rencontres de Moriond `Electronic Correlations: From Meso- to
Nano-physics' Les Arcs, France January 20-27, 2001 [SPEC-S01/027
Magnetic-field-dependent quasiparticle energy relaxation in mesoscopic wires
In order to find out if magnetic impurities can mediate interactions between
quasiparticles in metals, we have measured the effect of a magnetic field B on
the energy distribution function f(E) of quasiparticles in two silver wires
driven out-of-equilibrium by a bias voltage U. In a sample showing sharp
distributions at B=0, no magnetic field effect is found, whereas in the other
sample, rounded distributions at low magnetic field get sharper as B is
increased, with a characteristic field proportional to U. Comparison is made
with recent calculations of the effect of magnetic-impurities-mediated
interactions taking into account Kondo physics.Comment: 4 pages, 3 figures, to be published in Physical Review Letter
Phase controlled superconducting proximity effect probed by tunneling spectroscopy
Using a dual-mode STM-AFM microscope operating below 50mK we measured the
Local Density of States (LDoS) along small normal wires connected at both ends
to superconductors with different phases. We observe that a uniform minigap can
develop in the whole normal wire and in the superconductors near the
interfaces. The minigap depends periodically on the phase difference. The
quasiclassical theory of superconductivity applied to a simplified 1D model
geometry accounts well for the data.Comment: Accepted for publication in Physical Review Letter
Hierarchical Wigner Crystal at the Edge of Quantum Hall Bar
We show that quasiholes persist near the edge of incompressible Quantum Hall
state forming a Wigner structure. The average density of quasiholes is fixed by
electrostatics and decreases slowly with increasing distance from the edge. As
we see from elementary reasoning, their specific arrangement can not be a
regular Wigner lattice and shows a complex hierarchical structure of
dislocations.Comment: LaTEX file. Ps figures upon reques
Supercurrent Spectroscopy of Andreev States
We measure the excitation spectrum of a superconducting atomic contact. In
addition to the usual continuum above the superconducting gap, the single
particle excitation spectrum contains discrete, spin-degenerate Andreev levels
inside the gap. Quasiparticle excitations are induced by a broadband on-chip
microwave source and detected by measuring changes in the supercurrent flowing
through the atomic contact. Since microwave photons excite quasiparticles in
pairs, two types of transitions are observed: Andreev transitions, which
consists of putting two quasiparticles in an Andreev level, and transitions to
odd states with a single quasiparticle in an Andreev level and the other one in
the continuum. In contrast to absorption spectroscopy, supercurrent
spectroscopy allows detection of long-lived odd states.Comment: typos correcte
Theory of microwave spectroscopy of Andreev bound states with a Josephson junction
We present a microscopic theory for the current through a tunnel Josephson
junction coupled to a non-linear environment, which consists of an Andreev
two-level system coupled to a harmonic oscillator. It models a recent
experiment [Bretheau, Girit, Pothier, Esteve, and Urbina, Nature (London) 499,
312 (2013)] on photon spectroscopy of Andreev bound states in a superconducting
atomic-size contact. We find the eigenenergies and eigenstates of the
environment and derive the current through the junction due to inelastic Cooper
pair tunneling. The current-voltage characteristic reveals the transitions
between the Andreev bound states, the excitation of the harmonic mode that
hybridizes with the Andreev bound states, as well as multi-photon processes.
The calculated spectra are in fair agreement with the experimental data.Comment: 8 pages, 6 figure
- …