Improving the stability of cryogenic current comparator setups

We have realized an improved resistance calibration setup based on a cryogenic current comparator (CCC). The comparator, with 18 windings and 4647 turns in total, is well-suited for all the necessary comparisons with a 100 Omega standard resistor with the quantum Hall effect and inside the range of standard resistance values from 1 Omega to 1 MOmega. The new state-of-the-art setup is equipped with a low-noise dc SQUID (superconducting quantum interference device) and a digital double current source. Proper damping of the CCC resonance, careful electronics design ('box-in-box') and application of internal wideband feedback to the SQUID sensor improve the dynamic stability considerably and lower the overall measurement time as compared against our previous setup.