Tunable Josephson Devices for Quantum Computation

We present the design and the performances of a
vertical Josephson interferometer, which can be inserted within
superconducting loops in order to obtain controllable Josephson
devices. The most interesting feature of the vertical interferometer
is that the Josephson current is precisely controlled by a small
transversal magnetic field parallel to the superconducting loop
plane and can be modulated from a maximum to zero with high
precision. This system can be used to realize a switchable flux
transformer to couple quantum bits when desired as well as
to vary the critical current of a flux qubit in situ. In the latter
application, the vertical interferometer is controlled by a magnetic
field orthogonal to the one applied to tilt the qubit potential, thus
minimizing the cross talking of the two magnetic fields.