Superconducting quantum interference proximity transistor

When a superconductor is placed close to a non-superconducting metal, it can induce superconducting correlations in the metal(1-10), known as the 'proximity effect'(11). Such behaviour modifies the density of states (DOS) in the normal metal(12-15) and opens a minigap(12,13,16) with an amplitude that can be controlled by changing the phase of the superconducting order parameter(12,15). Here, we exploit such behaviour to realize a new type of interferometer, the superconducting quantum interference proximity transistor (SQUIPT), for which the operation relies on the modulation with the magnetic field of the DOS of a proximized metal embedded in a superconducting loop. Even without optimizing its design, this device shows extremely low flux noise, down to similar to 10(-5) Phi(0)Hz(-1/2) (Phi(0) similar or equal to 2 x 10(-15) Wb is the flux quantum) and dissipation several orders of magnitude smaller than in conventional superconducting interferometers(17-19). With optimization, the SQUIPT could significantly increase the sensitivity with which small magnetic moments are detected.