3,031 research outputs found
High-gain weakly nonlinear flux-modulated Josephson parametric amplifier using a SQUID-array
We have developed and measured a high-gain quantum-limited microwave
parametric amplifier based on a superconducting lumped LC resonator with the
inductor L including an array of 8 superconducting quantum interference devices
(SQUIDs). This amplifier is parametrically pumped by modulating the flux
threading the SQUIDs at twice the resonator frequency. Around 5 GHz, a maximum
gain of 31 dB, a product amplitude-gain x bandwidth above 60 MHz, and a 1 dB
compression point of -123 dBm at 20 dB gain are obtained in the non-degenerate
mode of operation. Phase sensitive amplification-deamplification is also
measured in the degenerate mode and yields a maximum gain of 37 dB. The
compression point obtained is 18 dB above what would be obtained with a single
SQUID of the same inductance, due to the smaller nonlinearity of the SQUID
array.Comment: 7 pages, 4 figures, 23 reference
Superconducting single-mode contact as a microwave-activated quantum interferometer
The dynamics of a superconducting quantum point contact biased at subgap
voltages is shown to be strongly affected by a microwave electromagnetic field.
Interference among a sequence of temporally localized, microwave-induced
Landau-Zener transitions between current carrying Andreev levels results in
energy absorption and in an increase of the subgap current by several orders of
magnitude. The contact is an interferometer in the sense that the current is an
oscillatory function of the inverse bias voltage. Possible applications to
Andreev-level spectroscopy and microwave detection are discussed
Giant Josephson current through a single bound state in a superconducting tunnel junction
We study the microscopic structure of the Josephson current in a single-mode
tunnel junction with a wide quasiclassical tunnel barrier. In such a junction
each Andreev bound state carries a current of magnitude proportional to the
{\em amplitude} of the normal electron transmission through the junction.
Tremendous enhancement of the bound state current is caused by the resonance
coupling of superconducting bound states at both superconductor-insulator
interfaces of the junction. The possibility of experimental observation of the
single bound state current is discussed.Comment: 11 pages, [aps,preprint]{revtex
Resistively-shunted superconducting quantum point contacts
We have studied the Josephson dynamics of resistively-shunted ballistic
superconducting quantum point contacts at finite temperatures and arbitrary
number of conducting modes. Compared to the classical Josephson dynamics of
tunnel junctions, dynamics of quantum point contacts exhibits several new
features associated with temporal fluctuations of the Josephson potential
caused by fluctuations in the occupation of the current-carrying Andreev
levels.Comment: 5 pages, RevTex, 3 postscript figures include
Phonon relaxation of subgap levels in superconducting quantum point contacts
Superconducting quantum point contacts are known to possess two subgap states
per each propagating mode. In this note we compute the low-temperature
relaxation rate of the upper subgap state into the lower one with the emission
of an acoustic phonon. If the reflection in the contact is small, the
relaxation time may become much longer than the characteristic lifetime of a
bulk quasiparticle.Comment: REVTeX, 4 page
Review of the some specific features of the detecting of heavy recoils
In this paper, we present the results of the first beam tests of the
detection system at the focal plane of the Dubna Gas-Filled Recoil Separator-2
(DGFRS-2), which receives beams from the DC-280 FLNR cyclotron. The high beam
intensity of Ca heavy ions from the cyclotron enables us to
obtain a number of superheavy recoils sufficient to compare both the measured
and calculated spectra of superheavy recoils implanted into a silicon detector.
A real-time algorithm to search for an Evaporation Residue (ER) --
correlated sequences is described in brief. It should be noted that the DGFRS-2
spectrometer operates in conjunction with the 48x128 strip DSSD (Double-sided
Silicon Strip Detector; 48x226 mm2) detector and a low-pressure pentane-filled
gaseous detector (1.2 Torr; 80x230 mm). A block-diagram of the spectrometer
and the event format are also presented. Special attention is paid to the
response of a low-pressure pentane-filled DeltaE multiwire proportional chamber
for recoils of Fl, synthesized in the Pu+Ca Fl +3n
complete fusion nuclear reaction. Some actual parameters of the detection
system have also been extracted from Yb + Ca, Th +
Ca, Am + Ca, U + Ca reactions. The effect
of neighbor strip charge sharing for the ohmic side of the DSSD detector is
also under consideration.Comment: 18 page
Two-level Hamiltonian of a superconducting quantum point contact
In a superconducting quantum point contact, dynamics of the superconducting
phase is coupled to the transitions between the subgap states. We compute this
coupling and derive the two-level Hamiltonian of the contact.Comment: REVTeX, 5 pages, reference adde
Combined effect of Zeeman splitting and spin-orbit interaction on the Josephson current in a S-2DEG-S structure
We analyze new spin effects in current-carrying state of superconductor-2D
electron gas-superconductor (S-2DEG-S) device with spin-polarized nuclei in
2DEG region. The hyperfine interaction of 2D electrons with nuclear spins,
described by the effective magnetic field B, produces Zeeman splitting of
Andreev levels without orbital effects, that leads to the interference pattern
of supercurrent oscillations over B. The spin-orbit effects in 2DEG cause
strongly anisotropic dependence of the Josephson current on the direction of B,
which may be used as a probe for the spin-orbit interaction intensity. Under
certain conditions, the system reveals the properties of pi-junction.Comment: 4 pages, 4 figure
The Use of Bayesian Networks in Public Administration of the Economy
The state, exercising its managerial function in the
economic sphere, pursues specific goals, the main of which is to
ensure for society and the decent state welfare, as well as to
increase the level of material production. Bayesian trust networks
can be used in government project management as diagrams
reflecting the causal relationships between events or influence
diagrams. Besides, Bayesian trust networks allow integrating into
the model the data obtained at each stage of project development,
thereby providing feedback, which is an essential component of
the public administration
Non-adiabatic Josephson Dynamics in Junctions with in-Gap Quasiparticles
Conventional models of Josephson junction dynamics rely on the absence of low
energy quasiparticle states due to a large superconducting gap. With this
assumption the quasiparticle degrees of freedom become "frozen out" and the
phase difference becomes the only free variable, acting as a fictitious
particle in a local in time Josephson potential related to the adiabatic and
non-dissipative supercurrent across the junction. In this article we develop a
general framework to incorporate the effects of low energy quasiparticles
interacting non-adiabatically with the phase degree of freedom. Such
quasiparticle states exist generically in constriction type junctions with high
transparency channels or resonant states, as well as in junctions of
unconventional superconductors. Furthermore, recent experiments have revealed
the existence of spurious low energy in-gap states in tunnel junctions of
conventional superconductors - a system for which the adiabatic assumption
typically is assumed to hold. We show that the resonant interaction with such
low energy states rather than the Josephson potential defines nonlinear
Josephson dynamics at small amplitudes.Comment: 9 pages, 1 figur
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