Sensitivity and spatial resolution of square loop SQUID magnetometers

We calculate the flux threading the pick-up coil of a square SQUID magnetometer in the presence of a current dipole source. The result reproduces that of a circle coil magnetometer calculated by Wikswo with only small differences. However it has a simpler form so that it is possible to derive from it closed form expressions for the current dipole sensitivity and the spatial resolution. The results are useful to assess the overall performance of the device and to compare different designs

Topology-Induced Critical Current Enhancement in Josephson Networks

We investigate the properties of Josephson junction networks with inhomogeneous architecture. The networks are shaped as "quare comb" planar lattices on which Josephson junctions link superconducting islands arranged in the plane to generate the pertinent topology. Compared to the behavior of reference linear arrays, the temperature dependencies of the Josephson currents of the branches of the network exhibit relevant differences. The observed phenomena evidence new and surprising behavior of superconducting Josephson arrays as well as remarkable similarities with bosonic junction arrays.Comment: improved figures (added magnetic pattern and single junction switching) some changes in the text and in the titl

Resonance phenomena in the macroscopic quantum tunnelling

In this paper we present a theoretical approach to describe the quantum behaviour of a macroscopic system interacting with an external field at frequencies close to resonant condition. Moreover we apply our results to simulate resonant phenomena in rf SQUIDs, whose parameters lie in the range typically used in the experiments. © 2006 IOP Publishing Ltd

Resonance Phenomena in Macroscopic Quantum Tunneling: the small viscosity limit.

We present a theoretical study of the resonant quantum behavior for a macroscopic superconducting system interacting with an external microwave at proper frequency. Here we consider a system described by a double well potential, an rf-SQUID, in the extremely underdamped regime. Numerical simulations for resonant phenomena have been performed for this system, whose parameters belong to the range typically used in the experiments. The dependence of the transition probability W on the external drive of the system, φx, can show three resonance peaks, in a small microwave frequency range. One peak is connected with the anticrossing and the other two with the external microwave frequency ν. The relative position and the height of the two lateral peaks depend on the microwave frequency. This behavior is studied here for the first time

Observation of macroscopic quantum tunnelling in a rf superconducting quantum interference device system

We present the experimental observation of the effects of macroscopic quantum tunnelling in a SQUID device, consisting of a rf SQUID coupled to a readout system based on a dc SQUID sensor. Data on the decay rate from the metastable flux states of a if SQUID are reported, both in the classical and quantum regimes. The low dissipation level and the good insulation of the probe from external noise are encouraging in view of building a macroscopic quantum coherent system