APPLICATION OF QUANTUM SUPERCONDUCTIVITY TO A NEW KIND OF INSTRUMENTATION

Under the proper circumstances voltage can be developed across a superconductor-this voltage V is the electromotive force induced by flux flow through the superconducting material. Superconducting thin-film techniques have been developed to assure that this flow is composed of individual flux quanta. These techniques usually involve inhomogeneous superconductivity; the inhomogenity either being artificially generated by flow through a constriction (as a Dayem bridge) or intrinsic to the material itself (as a deliberate spacial modification of electron density, Notarys). This resulting superconducting structure may be thought of as a current controlled flux valve-passing quanta φ0 at a rate v=Vφ0-1. These flux valves have been incorporated into various circuits leading to results similar to the behavior of a Josephson Junction. In particular, inserting a valve into a superconducting ring produces a device similar to the Josephson Junction interferometer-highly sensitive to magnetic field. These devices have been adopted into several operating instruments: a differential magnetometer with a one-second time constant and field sensitivity 10-10 G, a digital magnetometer counting increments of 10-7 G at 104/sec, and a voltmeter with a 10-3-sec time constant and sensitivity of 10 -14 V. © 1969 The American Institute of Physics.