2,299 research outputs found
Classical analogs for Rabi-oscillations, Ramsey-fringes, and spin-echo in Josephson junctions
We investigate the results of recently published experiments on the quantum
behavior of Josephson circuits in terms of the classical modelling based on the
resistively and capacitively-shunted (RCSJ) junction model. Our analysis shows
evidence for a close analogy between the nonlinear behavior of a pulsed
microwave-driven Josephson junction at low temperature and low dissipation and
the experimental observations reported for the Josephson circuits.
Specifically, we demonstrate that Rabi-oscillations, Ramsey-fringes, and
spin-echo observations are not phenomena with a unique quantum interpretation.
In fact, they are natural consequences of transients to phase-locking in
classical nonlinear dynamics and can be observed in a purely classical model of
a Josephson junction when the experimental recipe for the application of
microwaves is followed and the experimental detection scheme followed. We
therefore conclude that classical nonlinear dynamics can contribute to the
understanding of relevant experimental observations of Josephson response to
various microwave perturbations at very low temperature and low dissipation.Comment: 16 pages, 7 figure
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
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
Inertial amplification of continuous structures: Large band gaps from small masses
Wave motion in a continuous elastic rod with a periodically attached
inertial-amplification mechanism is investigated. The mechanism has properties
similar to an "inerter" typically used in vehicle suspensions, however here it
is constructed and utilized in a manner that alters the intrinsic properties of
a continuous structure. The elastodynamic band structure of the hybrid
rod-mechanism structure yields band gaps that are exceedingly wide and deep
when compared to what can be obtained using standard local resonators, while
still being low in frequency. With this concept, a large band gap may be
realized with as much as twenty times less added mass compared to what is
needed in a standard local resonator configuration. The emerging inertially
enhanced continuous structure also exhibits unique qualitative features in its
dispersion curves. These include the existence of a characteristic double-peak
in the attenuation constant profile within gaps and the possibility of
coalescence of two neighbouring gaps creating a large contiguous gap.Comment: Manuscript is under review for journal publicatio
Proton Pump Activity of Mitochondria-rich Cells : The Interpretation of External Proton-concentration Gradients
We have hypothesized that a major role of the apical H+-pump in mitochondria-rich (MR) cells of amphibian skin is to energize active uptake of Clâ via an apical Clâ/HCO3â-exchanger. The activity of the H+ pump was studied by monitoring mucosal [H+]-profiles with a pH-sensitive microelectrode. With gluconate as mucosal anion, pH adjacent to the cornified cell layer was 0.98 Âą 0.07 (mean Âą SEM) pH-units below that of the lightly buffered bulk solution (pH = 7.40). The average distance at which the pH-gradient is dissipated was 382 Âą 18 Îźm, corresponding to an estimated âunstirred layerâ thickness of 329 Âą 29 Îźm. Mucosal acidification was dependent on serosal pCO2, and abolished after depression of cellular energy metabolism, confirming that mucosal acidification results from active transport of H+. The [H+] was practically similar adjacent to all cells and independent of whether the microelectrode tip was positioned near an MR-cell or a principal cell. To evaluate [H+]-profiles created by a multitude of MR-cells, a mathematical model is proposed which assumes that the H+ distribution is governed by steady diffusion from a number of point sources defining a set of particular solutions to Laplace's equation. Model calculations predicted that with a physiological density of MR cells, the [H+] profile would be governed by so many sources that their individual contributions could not be experimentally resolved. The flux equation was integrated to provide a general mathematical expression for an external standing [H+]âgradient in the unstirred layer. This case was treated as free diffusion of protons and proton-loaded buffer molecules carrying away the protons extruded by the pump into the unstirred layer; the expression derived was used for estimating stationary proton-fluxes. The external [H+]-gradient depended on the mucosal anion such as to indicate that base (HCO3â) is excreted in exchange not only for Cl â, but also for Brâ and Iâ, indicating that the active fluxes of these anions can be attributed to mitochondria-rich cells
Phase-Locking of Vortex Lattices Interacting with Periodic Pinning
We examine Shapiro steps for vortex lattices interacting with periodic
pinning arrays driven by AC and DC currents. The vortex flow occurs by the
motion of the interstitial vortices through the periodic potential generated by
the vortices that remain pinned at the pinning sites. Shapiro steps are
observed for fields B_{\phi} < B < 2.25B_{\phi} with the most pronouced steps
occuring for fields where the interstitial vortex lattice has a high degree of
symmetry. The widths of the phase-locked current steps as a function of the
magnitude of the AC driving are found to follow a Bessel function in agreement
with theory.Comment: 5 pages 5 postscript figure
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