1,688 research outputs found
Supercurrent-induced temperature gradient across a nonequilibrium SNS Josephson junction
Using tunneling spectroscopy, we have measured the local electron energy
distribution function in the normal part of a superconductor-normal
metal-superconductor (SNS) Josephson junction containing an extra lead to a
normal reservoir. In the presence of simultaneous supercurrent and injected
quasiparticle current, the distribution function exhibits a sharp feature at
very low energy. The feature is odd in energy, and odd under reversal of either
the supercurrent or the quasiparticle current direction. The feature represents
an effective temperature gradient across the SNS Josephson junction that is
controllable by the supercurrent.Comment: 4 pages, 4 figures, corrected typos, added plot to figure
Normal metal - superconductor tunnel junction as a Brownian refrigerator
Thermal noise generated by a hot resistor (resistance ) can, under proper
conditions, catalyze heat removal from a cold normal metal (N) in contact with
a superconductor (S) via a tunnel barrier. Such a NIS junction acts as
Maxwell's demon, rectifying the heat flow. Upon reversal of the temperature
gradient between the resistor and the junction the heat fluxes are reversed:
this presents a regime which is not accessible in an ordinary voltage-biased
NIS structure. We obtain analytical results for the cooling performance in an
idealized high impedance environment, and perform numerical calculations for
general . We conclude by assessing the experimental feasibility of the
proposed effect
Effect of Magnetic Impurities on Energy Exchange between Electrons
In order to probe quantitatively the effect of Kondo impurities on energy
exchange between electrons in metals, we have compared measurements on two
silver wires with dilute magnetic impurities (manganese) introduced in one of
them. The measurement of the temperature dependence of the electron phase
coherence time on the wires provides an independent determination of the
impurity concentration. Quantitative agreement on the energy exchange rate is
found with a theory by G\"{o}ppert et al. that accounts for Kondo scattering of
electrons on spin-1/2 impurities.Comment: 4 page
Density of states in a superconductor carrying a supercurrent
We have measured the tunneling density of states (DOS) in a superconductor
carrying a supercurrent or exposed to an external magnetic field. The pair
correlations are weakened by the supercurrent, leading to a modification of the
DOS and to a reduction of the gap. As predicted by the theory of
superconductivity in diffusive metals, we find that this effect is similar to
that of an external magnetic field.Comment: To be published in Physical Review Letter
The Bright Side of Coulomb Blockade
We explore the photonic (bright) side of dynamical Coulomb blockade (DCB) by
measuring the radiation emitted by a dc voltage-biased Josephson junction
embedded in a microwave resonator. In this regime Cooper pair tunneling is
inelastic and associated to the transfer of an energy 2eV into the resonator
modes. We have measured simultaneously the Cooper pair current and the photon
emission rate at the resonance frequency of the resonator. Our results show two
regimes, in which each tunneling Cooper pair emits either one or two photons
into the resonator. The spectral properties of the emitted radiation are
accounted for by an extension to DCB theory.Comment: 4 pages, 4 figures + 3 pages, 1 figure supplementary materia
Experimental Test of the Dynamical Coulomb Blockade Theory for Short Coherent Conductors
We observed the recently predicted quantum suppression of dynamical Coulomb
blockade on short coherent conductors by measuring the conductance of a quantum
point contact embedded in a tunable on-chip circuit. Taking advantage of the
circuit modularity we measured most parameters used by the theory. This allowed
us to perform a reliable and quantitative experimental test of the theory.
Dynamical Coulomb blockade corrections, probed up to the second conductance
plateau of the quantum point contact, are found to be accurately normalized by
the same Fano factor as quantum shot noise, in excellent agreement with the
theoretical predictions.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Quantum nondemolition-like, fast measurement scheme for a superconducting qubit
We present a measurement protocol for a flux qubit coupled to a
dc-Superconducting QUantum Interference Device (SQUID), representative of any
two-state system with a controllable coupling to an harmonic oscillator
quadrature, which consists of two steps. First, the qubit state is imprinted
onto the SQUID via a very short and strong interaction. We show that at the end
of this step the qubit dephases completely, although the perturbation of the
measured qubit observable during this step is weak. In the second step,
information about the qubit is extracted by measuring the SQUID. This step can
have arbitrarily long duration, since it no longer induces qubit errors.Comment: published version, minor correction
Using a quantum dot as a high-frequency shot noise detector
We present the experimental realization of a Quantum Dot (QD) operating as a
high-frequency noise detector. Current fluctuations produced in a nearby
Quantum Point Contact (QPC) ionize the QD and induce transport through excited
states. The resulting transient current through the QD represents our detector
signal. We investigate its dependence on the QPC transmission and voltage bias.
We observe and explain a quantum threshold feature and a saturation in the
detector signal. This experimental and theoretical study is relevant in
understanding the backaction of a QPC used as a charge detector.Comment: 4 pages, 4 figures, accepted for publication in Physical Review
Letter
Brownian refrigeration by hybrid tunnel junctions
Voltage fluctuations generated in a hot resistor can cause extraction of heat
from a colder normal metal electrode of a hybrid tunnel junction between a
normal metal and a superconductor. We extend the analysis presented in [Phys.
Rev. Lett. 98, 210604 (2007)] of this heat rectifying system, bearing
resemblance to a Maxwell's demon. Explicit analytic calculations show that the
entropy of the total system is always increasing. We then consider a single
electron transistor configuration with two hybrid junctions in series, and show
how the cooling is influenced by charging effects. We analyze also the cooling
effect from nonequilibrium fluctuations instead of thermal noise, focusing on
the shot noise generated in another tunnel junction. We conclude by discussing
limitations for an experimental observation of the effect.Comment: 16 pages, 16 figure
- …