1,185 research outputs found
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
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
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
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
Tunnel Spectroscopy of a Proximity Josephson Junction
We present tunnel spectroscopy experiments on the proximity effect in lateral
superconductor-normal metal-superconductor (SNS) Josephson junctions. Our weak
link is embedded into a superconducting (S) ring allowing phase biasing of the
Josephson junction by an external magnetic field. We explore the temperature
and phase dependence of both the induced mini-gap and the modification of the
density of states in the normal (N) metal. Our results agree with a model based
on the quasiclassical theory in the diffusive limit. The device presents an
advanced version of the superconducting quantum interference proximity
transistor (SQUIPT), now reaching flux sensitivities of 3 nA where
is the flux quantum.Comment: 5 pages, 4 figure
Vanishing quasiparticle density in a hybrid Al/Cu/Al single-electron transistor
The achievable fidelity of many nanoelectronic devices based on
superconducting aluminum is limited by either the density of residual
nonequilibrium quasiparticles n_qp or the density of quasiparticle states in
the gap, characterized by Dynes parameter \gamma. We infer upper bounds n_qp <
0.033 um^-3 and \gamma < 1.6*10^-7 from transport measurements performed on
Al/AlOx/Cu single-electron transistors, improving previous results by an order
of magnitude. Owing to efficient microwave shielding and quasiparticle
relaxation, typical number of quasiparticles in the superconducting leads is
zero.Comment: 5 pages, 3 figures; updated to revised version that was accepted for
publication, contains data from a reference sample without qp trap
Crossover from weak to strong coupling regime in dispersive circuit QED
We study the decoherence of a superconducting qubit due to the dispersive
coupling to a damped harmonic oscillator. We go beyond the weak
qubit-oscillator coupling, which we associate with a phase Purcell effect, and
enter into a strong coupling regime, with qualitatively different behavior of
the dephasing rate. We identify and give a physicaly intuitive discussion of
both decoherence mechanisms. Our results can be applied, with small
adaptations, to a large variety of other physical systems, e. g. trapped ions
and cavity QED, boosting theoretical and experimental decoherence studies.Comment: Published versio
AC Josephson effect and resonant Cooper pair tunneling emission of a Cooper Pair Transistor
We measure the high-frequency emission of a single Cooper pair
transistor(SCPT) in the regime where transport is only due to tunneling of
Cooper pairs. This is achieved by coupling on-chip the SCPT to a
superconductor-insulator-superconductor junction and by measuring the photon
assisted tunneling current of quasiparticles across the junction. This
technique allows a direct detection of the AC Josephson effect of the SCPT and
provides evidence of Landau-Zener transitions for proper gate voltage. The
emission in the regime of resonant Cooper pair tunneling is also investigated.
It is interpreted in terms of transitions between charge states coupled by the
Josephson effect.Comment: Revtex4, 5 pages, 4 figures, final versio
Confinement of electrons in layered metals
We analyze the out of plane hopping in models of layered systems where the
in--plane properties deviate from Landau's theory of a Fermi liquid. We show
that the hopping term acquires a non trivial energy dependence, due to the
coupling to in plane excitations, and can be either relevant or irrelevant at
low energies or temperatures. The latter is always the case if the Fermi level
lies close to a saddle point in the dispersion relation.Comment: 4 pages, 1 eps figur
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