95 research outputs found
Direct current superconducting quantum interferometers with asymmetric shunt resistors
We have investigated asymmetrically shunted Nb/Al-AlO/Nb direct current
(dc) superconducting quantum interference devices (SQUIDs). While keeping the
total resistance identical to a comparable symmetric SQUID with , we shunted only one of the two Josephson junctions with
. Simulations predict that the optimum energy resolution
and thus also the noise performance of such an asymmetric SQUID can
be 3--4 times better than that of its symmetric counterpart. Experiments at a
temperature of 4.2\,K yielded for an asymmetric
SQUID with an inductance of . For a comparable symmetric device
was achieved, confirming our simulation results.Comment: 5 pages, 4 figure
Spectroscopy of a fractional Josephson vortex molecule
In long Josephson junctions with multiple discontinuities of the Josephson
phase, fractional vortex molecules are spontaneously formed. At each
discontinuity point a fractional Josephson vortex carrying a magnetic flux
, Wb being the magnetic flux
quantum, is pinned. Each vortex has an oscillatory eigenmode with a frequency
that depends on and lies inside the plasma gap.
We experimentally investigate the dependence of the eigenfrequencies of a
two-vortex molecule on the distance between the vortices, on their topological
charge and on the bias current applied to the
Josephson junction. We find that with decreasing distance between vortices, a
splitting of the eigenfrequencies occurs, that corresponds to the emergence of
collective oscillatory modes of both vortices. We use a resonant microwave
spectroscopy technique and find good agreement between experimental results and
theoretical predictions.Comment: submitted to Phys. Rev.
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
Wirkung des Gluonenkondensats auf ein Bindungssystem von schweren Quark und Antiquark
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