426 research outputs found
Dynamics of An Underdamped Josephson Junction Ladder
We show analytically that the dynamical equations for an underdamped ladder
of coupled small Josephson junctions can be approximately reduced to the
discrete sine-Gordon equation. As numerical confirmation, we solve the coupled
Josephson equations for such a ladder in a magnetic field. We obtain
discrete-sine-Gordon-like IV characteristics, including a flux flow and a
``whirling'' regime at low and high currents, and voltage steps which represent
a lock-in between the vortex motion and linear ``phasons'', and which are
quantitatively predicted by a simple formula. At sufficiently high anisotropy,
the fluxons on the steps propagate ballistically.Comment: 11pages, latex, no figure
Aluminum Hard Mask Technique for the Fabrication of High-Quality Submicron Nb/Al-AlOx/Nb Josephson Junctions
We have developed a combined photolithography and electron-beam lithography
fabrication process for sub-\mum to \mum-size Nb/Al-AlOx/Nb Josephson
junctions. In order to define the junction size and protect its top electrode
during anodic oxidation, we developed and used the new concept of an aluminum
hard mask. Josephson junctions of sizes down to 0.5 \mum2 have been fabricated
and thoroughly characterized. We found that they have a very high quality,
which is witnessed by the IV curves with quality parameters Vm > 50 mV and Vgap
= 2.8 mV at 4.2 K, as well as IcRN products of 1.75-1.93 mV obtained at lower
temperatures. In order to test the usability of our fabrication process for
superconducting quantum bits, we have also designed, fabricated and
experimentally investigated phase qubits made of these junctions. We found a
relaxation time of T1 = 26 ns and a dephasing time of T2 = 21 ns
In-situ bandaged Josephson junctions for superconducting quantum processors
Shadow evaporation is commonly used to micro-fabricate the key element of superconducting qubits—the Josephson junction. However, in conventional two-angle deposition circuit topology, unwanted stray Josephson junctions are created which contribute to dielectric loss. So far, this could be avoided by shorting the stray junctions with a so-called bandage layer deposited in an additional lithography step, which may further contaminate the chip surface. Here, we present an improved shadow evaporation technique allowing one to fabricate sub-micrometer-sized Josephson junctions together with bandage layers in a single lithography step. We also show that junction aging is significantly reduced when junction electrodes are passivated in an oxygen atmosphere directly after deposition
Whispering Vortices
Experiments indicating the excitation of whispering gallery type
electromagnetic modes by a vortex moving in an annular Josephson junction are
reported. At relativistic velocities the Josephson vortex interacts with the
modes of the superconducting stripline resonator giving rise to novel
resonances on the current-voltage characteristic of the junction. The
experimental data are in good agreement with analysis and numerical
calculations based on the two-dimensional sine--Gordon model.Comment: 5 pages, 5 figures, text shortened to fit 4 pages, correction of
typo
Nonreciprocal transmission of microwaves through a long Josephson junction
Nonreciprocal microwave transmission through a long Josephson junction in the
flux-flow regime is studied analytically and numerically within the framework
of the perturbed sine-Gordon model. We demonstrate that the maximum attenuation
of the transmitted power occurs when the direction of the flux flow is opposite
to the direction of the microwave propagation. This attenuation is
nonreciprocal with respect to the flux-flow direction and can be enhanced by
increasing the system length and proper impedance matching of the junction ends
to external transmission line.Comment: 5 pages, 5 figure
Dynamics and transformations of Josephson vortex lattice in layered superconductors
We consider dynamics of Josephson vortex lattice in layered superconductors
with magnetic, charge (electrostatic) and charge-imbalance (quasiparticle)
interactions between interlayer Josephson junctions taken into account. The
macroscopic dynamical equations for interlayer Josephson phase differences,
intralayer charge and electron-hole imbalance are obtained and used for
numerical simulations. Different transformations of the vortex lattice
structure are observed. It is shown that the additional dissipation due to the
charge imbalance relaxation leads to the stability of triangular lattice.Comment: 9 pages, 3 eps figures, to be published in Phys. Rev.
Broken symmetry of row switching in 2D Josephson junction arrays
We present an experimental and theoretical study of row switching in
two-dimensional Josephson junction arrays. We have observed novel dynamic
states with peculiar percolative patterns of the voltage drop inside the
arrays. These states were directly visualized using laser scanning microscopy
and manifested by fine branching in the current-voltage characteristics of the
arrays. Numerical simulations show that such percolative patterns have an
intrinsic origin and occur independently of positional disorder. We argue that
the appearance of these dynamic states is due to the presence of various
metastable superconducting states in arrays.Comment: 4 Pages, 6 Figure
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