Andreev Probe of Persistent Current States in Superconducting Quantum Circuits

Using the extraordinary sensitivity of Andreev interferometers to the superconducting phase difference associated with currents, we measure the persistent current quantum states in superconducting loops interrupted by Josephson junctions. Straightforward electrical resistance measurements of the interferometers give continuous read-out of the states, allowing us to construct the energy spectrum of the quantum circuit. The probe is estimated to be more precise and faster than previous methods, and can measure the local phase difference in a wide range of superconducting circuits.Comment: Changes made in light of referees comments; to appear in PR

"Giant" Aharonov-Bohm effect in mesoscopic silver rings with bismuth electrodes

Aharonov-Bohm resistance oscillations of mesoscopic silver rings are found to be enhanced $\sim 100$ times when contact to the ring is made with bismuth rather than silver or gold electrodes. An argument based on the idea that a mismatch of the Fermi surfaces at the interfaces leads to a reduced effective electrode size is shown to be inadequate, as the resistance oscillations exceed the maximum theoretical value of Altshuler, Aronov and Spivak (1991) by an order of magnitude