28 research outputs found
High performance magnetic field sensor based on Superconducting Quantum Interference Filters
We have developed an absolute magnetic field sensor using Superconducting
Quantum Interference Filter (SQIF) made of high-T_c grain boundary Josephson
junctions. The device shows the typical magnetic field dependent voltage
response V(B), which is sharp delta-like dip in the vicinity of zero magnetic
field. When the SQIF is cooled with magnetic shield, and then the shield is
removed, the presence of the ambient magnetic field induces a shift of the dip
position from B_0 ~ 0 to a value B ~ B_1, which is about the average value of
the earth magnetic field, at our latitude. When the SQIF is cooled in the
ambient field without shielding, the dip is first found at B ~ B_1, and the
further shielding of the SQIF results in a shift of the dip towards B_0 ~ 0.
The low hysteresis observed in the sequence of experiments (less than 5% of
B_1) makes SQIFs suitable for high precision measurements of the absolute
magnetic field. The experimental results are discussed in view of potential
applications of high-T_c SQIFs in magnetometry.Comment: 4 pages, 2 figure
Quadratic Mixing of Radio Frequency Signals using Superconducting Quantum Interference Filters
The authors demonstrate quadratic mixing of weak time harmonic
electromagnetic fields applied to Superconducting Quantum Interference Filters,
manufactured from high- grain boundary Josephson junctions and
operated in active microcooler. The authors use the parabolic shape of the dip
in the dc-voltage output around B=0 to mix \emph{quadratically} two external
rf-signals, at frequencies and well below the
Josephson frequency , and detect the corresponding mixing
signal at . Quadratic mixing takes also place when the SQIF
is operated without magnetic shield. The experimental results are well
described by a simple analytical model based on the adiabatic approximation.Comment: 3 pages, 3 figure
Effects of magnetic field on two-dimensional Superconducting Quantum Interference Filters
We present an experimental study of two-dimensional superconducting quantum
interference filters (2D-SQIFs) in the presence of a magnetic field B. The
dependences of the dc voltage on the applied magnetic field are characterized
by a unique delta-like dip at B=0, which depends on the distribution of the
areas of the individual loops, and on the bias current. The voltage span of the
dip scales proportional to the number of rows simultaneously operating at the
same working point. In addition, the voltage response of the 2D-SQIF is
sensitive to a field gradient generated by a control line and superimposed to
the homogeneous field coil. This feature opens the possibility to use 2D
superconducting quantum interference filters as highly sensitive detectors of
spatial gradients of magnetic field.Comment: 3 pages, 4 figures, submitted to AP
Two tone response of radiofrequency signals using the voltage output of a Superconducting Quantum Interference Filter
In the presence of weak time harmonic electromagnetic fields, Superconducting
Quantum Interference Filters (SQIFs) show the typical behavior of non linear
mixers. The SQIFs are manufactured from high-T_c grain boundary Josephson
junctions and operated in active microcooler. The dependence of dc voltage
output V_dc vs. static external magnetic field B is non-periodic and consists
of a well pronounced unique dip at zero field, with marginal side modulations
at higher fields. We have successfully exploited the parabolic shape of the
voltage dip around B=0 to mix quadratically two external time harmonic
rf-signals, at frequencies f_1 and f_2 below the Josephson frequency f_J, and
detect the corresponding mixing signal at f_1-f_2. When the mixing takes place
on the SQIF current-voltage characteristics the component at 2f_2 - f_1 is
present. The experiments suggest potential applications of a SQIF as a
non-linear mixing device, capable to operate at frequencies from dc to few GHz
with a large dynamic range.Comment: 10 pages, 3 Figures, submitted to J. Supercond. (as proceeding of the
HTSHFF Symposium, June 2006, Cardiff
Tailoring discrete quantum walk dynamics via extended initial conditions: Towards homogeneous probability distributions
We study the evolution of initially extended distributions in the coined
quantum walk on the line by analyzing the dispersion relation of the process
and its associated wave equations. This allows us, in particular, to devise an
initially extended condition leading to a uniform probability distribution
whose width increases linearly with time, with increasing homogeneity.Comment: 4 pages, 2 figure
The particle in the box: Intermode traces in the propagator
Characteristic structures such as canals and ridges-intermode traces-emerge in the spacetime representation of the probability distribution of a particle in a one-dimensional box. We show that the corresponding propagator already contains these structures. We relate their visibility to the factorization property of the initial wave packet
Shortcuts to adiabaticity in a time-dependent box
A method is proposed to drive an ultrafast non-adiabatic dynamics of an
ultracold gas trapped in a box potential. The resulting state is free from
spurious excitations associated with the breakdown of adiabaticity, and
preserves the quantum correlations of the initial state up to a scaling factor.
The process relies on the existence of an adiabatic invariant and the inversion
of the dynamical self-similar scaling law dictated by it. Its physical
implementation generally requires the use of an auxiliary expulsive potential
analogous to those used in soliton control. The method is extended to a broad
family of many-body systems. As illustrative examples we consider the ultrafast
expansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in
different dimensions, where the method exhibits an excellent robustness against
different regimes of interactions and the features of an experimentally
realizable box potential.Comment: 6 pp, 4 figures, typo in Eq. (6) fixe