535 research outputs found
Combined chips for atom-optics
We present experiments with Bose-Einstein condensates on a combined atom
chip. The combined structure consists of a large-scale "carrier chip" and
smaller "atom-optics chips", containing micron-sized elements. This allows us
to work with condensates very close to chip surfaces without suffering from
fragmentation or losses due to thermally driven spin flips. Precise
three-dimensional positioning and transport with constant trap frequencies are
described. Bose-Einstein condensates were manipulated with submicron accuracy
above atom-optics chips. As an application of atom chips, a direction sensitive
magnetic field microscope is demonstrated.Comment: 9 pages, 9 figure
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
Enhancing the critical current in quasiperiodic pinning arrays below and above the matching magnetic flux
Quasiperiodic pinning arrays, as recently demonstrated theoretically and
experimentally using a five-fold Penrose tiling, can lead to a significant
enhancement of the critical current Ic as compared to "traditional" regular
pinning arrays. However, while regular arrays showed only a sharp peak in
Ic(Phi) at the matching flux Phi1 and quasiperiodic arrays provided a much
broader maximum at Phi<Phi1, both types of pinning arrays turned out to be
inefficient for fluxes larger than Phi1. We demonstrate theoretically and
experimentally the enhancement of Ic(Phi) for Phi>Phi1 by using non-Penrose
quasiperiodic pinning arrays. This result is based on a qualitatively different
mechanism of flux pinning by quasiperiodic pinning arrays and could be
potentially useful for applications in superconducting micro-electronic devices
operating in a broad range of magnetic fields.Comment: 7 pages, 4 figure
0-pi Josephson tunnel junctions with ferromagnetic barrier
We fabricated high quality Nb/Al_2O_3/Ni_{0.6}Cu_{0.4}/Nb
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions.
Using a ferromagnetic layer with a step-like thickness, we obtain a 0-pi
junction, with equal lengths and critical currents of 0 and pi parts. The
ground state of our 330 microns (1.3 lambda_J) long junction corresponds to a
spontaneous vortex of supercurrent pinned at the 0-pi step and carrying ~6.7%
of the magnetic flux quantum Phi_0. The dependence of the critical current on
the applied magnetic field shows a clear minimum in the vicinity of zero field.Comment: submitted to PR
Critical current diffraction pattern of SIFS Josephson junctions with step-like F-layer
We present the latest generation of
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions
with a step-like thickness of the ferromagnetic (F) layer. The F-layer
thicknesses and in both halves were varied to obtain different
combinations of positive and negative critical current densities and
. The measured dependences of the critical current on applied magnetic
field can be well described by a model which takes into account different
critical current densities (obtained from reference junctions) and different
net magnetization of the multidomain ferromagnetic layer in both halves.Comment: 7 pages, 3 figure
Suppression of dissipation in Nb thin films with triangular antidot arrays by random removal of pinning sites
The depinning current Ic versus applied magnetic field B close to the
transition temperature Tc of Nb thin films with randomly diluted triangular
arrays of antidots is investigated. % Our experiments confirm essential
features in Ic(B) as predicted by Reichhardt and Olson Reichhardt [Phys.Rev. B
76, 094512 (2007)]. % We show that, by introducing disorder into periodic
pinning arrays, Ic can be enhanced. % In particular, for arrays with fixed
density n_p of antidots, an increase in dilution Pd induces an increase in Ic
and decrease of the flux-flow voltage for B>Bp=n_p Phi_0.Comment: 5 pages, 4 figure
Diffraction of a Bose-Einstein condensate from a Magnetic Lattice on a Micro Chip
We experimentally study the diffraction of a Bose-Einstein condensate from a
magnetic lattice, realized by a set of 372 parallel gold conductors which are
micro fabricated on a silicon substrate. The conductors generate a periodic
potential for the atoms with a lattice constant of 4 microns. After exposing
the condensate to the lattice for several milliseconds we observe diffraction
up to 5th order by standard time of flight imaging techniques. The experimental
data can be quantitatively interpreted with a simple phase imprinting model.
The demonstrated diffraction grating offers promising perspectives for the
construction of an integrated atom interferometer.Comment: 4 pages, 4 figure
High quality ferromagnetic 0 and pi Josephson tunnel junctions
We fabricated high quality \Nb/\Al_2\O_3/\Ni_{0.6}\Cu_{0.4}/\Nb
superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions.
Depending on the thickness of the ferromagnetic \Ni_{0.6}\Cu_{0.4} layer and
on the ambient temperature, the junctions were in the 0 or ground state.
All junctions have homogeneous interfaces showing almost perfect Fraunhofer
patterns. The \Al_2\O_3 tunnel barrier allows to achieve rather low damping,
which is desired for many experiments especially in the quantum domain. The
McCumber parameter increases exponentially with decreasing
temperature and reaches at . The critical
current density in the state was up to at , resulting in a Josephson penetration depth as low as
. Experimentally determined junction parameters are well
described by theory taking into account spin-flip scattering in the
\Ni_{0.6}\Cu_{0.4} layer and different transparencies of the interfaces.Comment: Changed content and Corrected typo
- …