Direct current inductance bridge for current-quantum-phase measurements in superconductors

A zero-frequency inductance bridge has been constructed for measurement of the inductance of superconducting circuit elements. The null detector uses a quantum magnetometer. The bridge is balanced by resistance adjustments at room temperature and gives directly the inductance or the quantum phase difference versus the current across the unknown superconducting element. The bridge has been used to measure kinetic inductors with 4×10−7 H to one part in 104 with a measuring current of 5×10−6 A.