  In this article we review the basic theoretical properties of a hybrid
superconducting interferometer which exploits the phase dependence of the
density of states of a metallic nanowire placed in good electric contact with a
superconductor to achieve high sensitivity to magnetic flux. The operation of a
prototype structure based on this principle, the superconducting quantum
interference proximity transistor (SQUIPT), has been recently reported. Limited
power dissipation joined with the opportunity to access single-spin detection
make this interferometer attractive for the investigation of the switching
dynamics of individual magnetic nanoparticles. The noise behavior of the device
is presented as well, where the feasibility of this structure as a single-spin
detector is also briefly addressed. In the final part we present the response
of a real SQUIPT device.
