160 research outputs found
Self-consistent dynamics of a Josephson junction in presence of an arbitrary environment
We derive microscopically the dynamics associated with the d.c. Josephson
effect in a superconducting tunnel junction interacting with an arbitrary
electromagnetic environment. To do so, we extend to superconducting junctions
the so-called P(E) theory (see e.g. Ingold and Nazarov, arXiv:cond-mat/0508728)
that accurately describes the interaction of a nonsuperconducting tunnel
junction with its environment. We show the dynamics of this system is described
by a small set of coupled correlation functions that take into account both
Cooper pair and quasiparticle tunneling. When the phase fluctuations are small
the problem is fully solved self-consistently, using and providing the exact
linear admittance Y({\omega}) of the interacting junction.Comment: 7 pages, 1 figur
Micro-fabricated electromagnetic filters for millikelvin experiments
In this article we report on the design, fabrication and tests of
micro-fabricated broadband filters suitable for proper electromagnetic
thermalization of electrical lines connected to sensitive quantum electronics
experiments performed at dilution fridge temperatures. Compared to previous
such miniature filters, the new design improves on performance and reliability.
These filters can be packed in space-saving cases with either single or
multi-contact connectors. Measured performance in the accessible range compares
well to simulations. We use these simulations to discuss the effectiveness of
these filters for electromagnetic thermalization at 30 mK.Comment: Available at http://www-spht.cea.fr/articles/s06/03
Interacting electrodynamics of short coherent conductors in quantum circuits
When combining lumped mesoscopic electronic components to form a circuit,
quantum fluctuations of electrical quantities lead to a non-linear
electromagnetic interaction between the components that is not generally
understood. The Landauer-B\"uttiker formalism that is frequently used to
describe non-interacting coherent mesoscopic components is not directly suited
to describe such circuits since it assumes perfect voltage bias, i.e. the
absence of fluctuations. Here, we show that for short coherent conductors of
arbitrary transmission, the Landauer-B\"uttiker formalism can be extended to
take into account quantum voltage fluctuations similarly to what is done for
tunnel junctions. The electrodynamics of the whole circuit is then formally
worked out disregarding the non-Gaussianity of fluctuations. This reveals how
the aforementioned non-linear interaction operates in short coherent
conductors: voltage fluctuations induce a reduction of conductance through the
phenomenon of dynamical Coulomb blockade but they also modify their internal
density of states leading to an additional electrostatic modification of the
transmission. Using this approach we can account quantitatively for conductance
measurements performed on Quantum Point Contacts in series with impedances of
the order of . Our work should enable a better engineering of
quantum circuits with targeted properties
Quantum Properties of the radiation emitted by a conductor in the Coulomb Blockade Regime
We present an input-output formalism describing a tunnel junction strongly
coupled to its electromagnetic environment. We exploit it in order to
investigate the dynamics of the radiation being emitted and scattered by the
junction. We find that the non-linearity imprinted in the electronic transport
by a properly designed environment generates strongly squeezed radiation. Our
results show that the interaction between a quantum conductor and
electromagnetic fields can be exploited as a resource to design simple sources
of non-classical radiation.Comment: 14 pages, 4 figures, includes Supplementar
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
Dynamical Coulomb Blockade of Shot Noise
We observe the suppression of the finite frequency shot-noise produced by a
voltage biased tunnel junction due to its interaction with a single
electromagnetic mode of high impedance. The tunnel junction is embedded in a
quarter wavelength resonator containing a dense SQUID array providing it with a
characteristic impedance in the kOhms range and a resonant frequency tunable in
the 4-6 GHz range. Such high impedance gives rise to a sizeable Coulomb
blockade on the tunnel junction (roughly 30% reduction in the differential
conductance) and allows an efficient measurement of the spectral density of the
current fluctuations at the resonator frequency. The observed blockade of
shot-noise is found in agreement with an extension of the dynamical Coulomb
blockade theory
Room-temperature tunnel current amplifier and experimental setup for high resolution electronic spectroscopy in millikelvin STM experiments
The spectroscopic resolution of tunneling measurements performed with a
scanning tunneling microscope is ultimately limited by the temperature at which
the experiment is performed. To take advantage of the potential high
spectroscopic resolution associated with operating an STM in a dilution
refrigerator we have designed a room temperature tunnel current amplifier
having very small back-action on the tunnel contact and allowing to nearly
reach the predicted energy resolution. This design is a modification of the
standard op-amp based tip-biasing current-voltage converter which implements
differential voltage sensing and whose back action on the tip voltage is only
~2 V rms for a 14 MV/A transimpedance and 22 kHz bandwidth.Comment: Available at http://www-spht.cea.fr/articles/s06/03
Effect of the Tunneling Conductance on the Coulomb Staircase
Quantum fluctuations of the charge in the single electron box are
investigated. The rounding of the Coulomb staircase caused by virtual electron
tunneling is determined by perturbation theory up to third order in the
tunneling conductance and compared with precise Monte Carlo data computed with
a new algorithm. The remarkable agreement for large conductance indicates that
presently available experimental data on Coulomb charging effects in metallic
nanostructures can be well explained by finite order perturbative results.Comment: 4 pages, 5 figure
Proximity Induced Josephson-Quasiparticle Process in a Single Electron Transistor
We have performed the first experiments in a superconductor - normal metal -
superconductor single electron transistor in which there is an extra
superconducting strip partially overlapping the normal metal island in good
metal-to-metal contact. Superconducting proximity effect gives rise to current
peaks at voltages below the quasiparticle threshold. We interpret these peaks
in terms of the Josephson-quasiparticle process and discuss their connection
with the proximity induced energy gap in the normal metal island.Comment: 4 pages + 4 figure
High Temperature Conductance of the Single Electron Transistor
The linear conductance of the single electron transistor is determined in the
high temperature limit. Electron tunneling is treated nonperturbatively by
means of a path integral formulation and the conductance is obtained from
Kubo's formula. The theoretical predictions are valid for arbitrary conductance
and found to explain recent experimental data.Comment: 4 pages, 2 figure
- …