Superconducting quantum interference proximity transistor with enhanced responsivity

We present an optimized superconducting quantum interference proximity transistor (SQUIPT) [1]. In such a device, a tunnel probe is placed in the middle of one weak link consisting of a lateral Josephson junction. The latter interrupts a superconducting ring and forms an Andreev interferometer based on the proximity effect [2]. Like this, one realizes the readout of the sensor independently from the ring itself by tunnel spectroscopy of the density of states within the weak link. Consequently, a SQUIPT has the advantage that the power dissipation during operation on the order of 1 fW allows an operation of the device with an electronic temperature of about 50 mK [3] or below. This is one key achievement with respect to the expected enhanced noise performance of the SQUIPT. The presented device has an optimized geometry and demonstrates now no hysteresis at the lowest temperatures as we increased the Josephson inductance of the weak link by decreasing its cross section. It has consequently almost one order of magnitude improved magnetic field responsivity.