Superconducting quantum interference proximity transistor

The development of superconducting quantum interference devices based on the Josephson effect has led to significant improvements in our ability to measure magnetic fields. A similar device, dubbed the superconducting quantum interference transistor, which exploits the proximity effect, could allow similar significant further improvements. When a superconductor is placed close to a non-superconducting metal, it can induce superconducting correlations in the metal 1,2,3,4,5,6,7,8,9,10, known as the ‘proximity effect’11. Such behaviour modifies the density of states (DOS) in the normal metal12,13,14,15 and opens a minigap12,13,16 with an amplitude that can be controlled by changing the phase of the superconducting order parameter12,15. 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 ∼10−5 Φ0Hz−1/2 (Φ0≃2×10−15 Wb is the flux quantum) and dissipation several orders of magnitude smaller than in conventional superconducting interferometers17,18,19. With optimization, the SQUIPT could significantly increase the sensitivity with which small magnetic moments are detected.