120 research outputs found
Magnetic Sensors Based on Long Josephson Tunnel Junctions - An Alternative to SQUIDs
The properties of Josephson devices are strongly affected by geometrical
effects. A loop-shaped superconducting electrode tightly couples a long
Josephson tunnel junction with the surrounding electromagnetic field. Due to
the fluxoid conservation, any change of the magnetic flux linked to the loop
results in a variation of the shielding current circulating around the loop,
which, in turn, affects the critical current of the Josephson junction. This
method allows the realization of a novel family of robust superconducting
devices (not based on the quantum interference) which can function as a
general-purpose magnetic sensors. The best performance is accomplished without
compromising the noise performance by employing an in-line-type junction few
times longer than its Josephson penetration length. The linear (rather than
periodic) response to magnetic flux changes over a wide range is just one of
its several advantages compared to the most sensitive magnetic detectors
currently available, namely the Superconducting Quantum Interference Devices
(SQUID). We will also comment on the drawbacks of the proposed system and
speculate on its noise properties.Comment: 13 pages, 4 figure
Multiple junction biasing of superconducting tunnel junction detectors
We describe a new biasing scheme for single photon detectors based on
superconducting tunnel junctions. It replaces a single detector junction with a
circuit of three junctions and achieves biasing of a detector junction at
subgap currents without the use of an external magnetic field. The biasing
occurs through the nonlinear interaction of the three junctions, which we
demonstrate through numerical simulation. This nonlinear state is numerically
stable against external fluctuations and is compatible with high fidelity
electrical readout of the photon-induced current. The elimination of the
external magnetic field potentially increases the capability of these types of
photon detectors and eases constraints involved in the fabrication of large
detector arrays.Comment: 15 pages, including 3 figure
Surgical Correction of Severe Bilateral Thumb Pincer-Nail Deformity
A 53 year old woman presented to the office with complaint of severe bilateral thumb nail pain and the deformity shown (Figure 1). She denied previous trauma to her thumb nails and had no history of previous bacterial or fungal infections of her nails. Based on the curvature of her nails, which increased from proximal to distal, a diagnosis of bilateral thumb pincer nail deformity was made
Investigation of low temperature quantum crossover in Josephson junctions
The evidence for macroscopic quantum tunneling (MQT) in Josephson junctions
at low temperatures has been reassessed. Swept bias escape distributions have
been modeled with an algorithm-based simulation and the results compared with
data from representative published experiments. Signatures expected of a
crossover to MQT are not found in the analyzed data.Comment: 7 pages, 6 figure
A classical statistical model for distributions of escape events in swept-bias Josephson junctions
We have developed a model for experiments in which the bias current applied
to a Josephson junction is slowly increased from zero until the junction
switches from its superconducting zero-voltage state, and the bias value at
which this occurs is recorded. Repetition of such measurements yields
experimentally determined probability distributions for the bias current at the
moment of escape. Our model provides an explanation for available data on the
temperature dependence of these escape peaks. When applied microwaves are
included we observe an additional peak in the escape distributions and
demonstrate that this peak matches experimental observations. The results
suggest that experimentally observed switching distributions, with and without
applied microwaves, can be understood within classical mechanics and may not
exhibit phenomena that demand an exclusively quantum mechanical interpretation.Comment: Eight pages, eight figure
Classical analysis of phase-locking transients and Rabi-type oscillations in microwave-driven Josephson junctions
We present a classical analysis of the transient response of Josephson
junctions perturbed by microwaves and thermal fluctuations. The results include
a specific low frequency modulation in phase and amplitude behavior of a
junction in its zero-voltage state. This transient modulation frequency is
linked directly to an observed variation in the probability for the system to
switch to its non-zero voltage state. Complementing previous work on linking
classical analysis to the experimental observations of Rabi-oscillations, this
expanded perturbation method also provides closed form analytical results for
attenuation of the modulations and the Rabi-type oscillation frequency. Results
of perturbation analysis are compared directly (and quantitatively) to
numerical simulations of the classical model as well as published experimental
data, suggesting that transients to phase-locking are closely related to the
observed oscillations.Comment: 18 pages total, 8 figures (typos corrected; minor revisions to
figures and equations
Investigation of resonant and transient phenomena in Josephson junction flux qubits
We present an analytical and computational study of resonances and transient
responses in a classical Josephson junction system. A theoretical basis for
resonances in a superconducting loop with three junctions is presented,
outlining both the direct relationship between the dynamics of single- and
multi-junction systems, and the direct relationships between observations of
the classical counterparts to Rabi oscillations, Ramsey fringes, and spin echo
oscillations in this class of systems. We show simulations data along with
analytical analyses of the classical model, and the results are related to
previously reported experiments conducted on three junction loops. We further
investigate the effect of off-resonant microwave perturbations to, e.g., the
Rabi-type response of the Josephson system, and we relate this response back to
the nonlinear and multi-valued resonance behavior previously reported for a
single Josephson junction. The close relationships between single and
multi-junction behavior demonstrates the underlying dynamical mechanism for a
whole class of classical counterparts to expected quantum mechanical
observations in a variety of systems; namely the resonant and transient
behavior of a particle in an anharmonic potential well with subsequent escape.Comment: 11 pages, seven figure
Screening magnetic fields by a superconducting disk: a simple model
We introduce a simple approach to evaluate the magnetic field distribution
around superconducting samples, based on the London equations; the elementary
variable is the vector potential. This procedure has no adjustable parameters,
only the sample geometry and the London length, , determine the
solution. The calculated field reproduces quantitatively the measured induction
field above MgB disks of different diameters, at 20K and for applied fields
lower than 0.4T. The model can be applied if the flux line penetration inside
the sample can be neglected when calculating the induction field distribution
outside the superconductor. Finally we show on a cup-shape geometry how one can
design a magnetic shield satisfying a specific constraint
Long Josephson Tunnel Junctions with Doubly Connected Electrodes
In order to mimic the phase changes in the primordial Big Bang, several
"cosmological" solid-state experiments have been conceived, during the last
decade, to investigate the spontaneous symmetry breaking in superconductors and
superfluids cooled through their transition temperature. In one of such
experiments the number of magnetic flux quanta spontaneously trapped in a
superconducting loop was measured by means of a long Josephson tunnel junction
built on top of the loop itself. We have analyzed this system and found a
number of interesting features not occurring in the conventional case with
simply connected electrodes. In particular, the fluxoid quantization results in
a frustration of the Josephson phase, which, in turn, reduces the junction
critical current. Further, the possible stable states of the system are
obtained by a self-consistent application of the principle of minimum energy.Comment: 34 pages, 9 figures, Phys. Rev. B April 201
Critical current in Nb-Cu-Nb junctions with non-ideal interfaces
We report on experimental studies of superconductor (Nb) - normal metal (Cu)
- superconductor (Nb) junctions with dirty interfaces between the different
materials. By using a set of simultaneously prepared samples, we investigated
the thickness dependence as well as the temperature dependence of the critical
currents in the junctions. Good agreement between the decay of the measured
critical currents and theoretical calculations was obtained without any fitting
parameters
- …