Cryogenic Electrical Metrology

Abstract

Low temperature operation offers precision electrical metrology a great variety of advantages compared with that using room temperature techniques. In the future, low temperature technology cannot be ignored in this field, so a few essentials of low temperature operation (see also [1]) should be listed here, without any claims to completeness:

• Quantum phenomena as fluxoid quantization [2], the Josephson effect [3] and the quantized Hall resistance in two dimensional electron gases [4].

• Optimum resolution for SQUIDs [5]; smallest action ΔH ≈ h (h Planck constant) makes possible detection of smallest magnetic fields, voltages, and electric currents.

• High-speed switching of SQUIDs in conjunction with extremely low power dissipation per switching operation form the basis for promising development of fast analog-to-digital converters [1] and fast cryo computers [6].

• Cryo-current comparators [7] with zero magnetic flux detection by means of a SQUID magnetometer enable precise current ratio measurements to be carried out with uncertainties of the order of 10⁻¹⁰.

• Use of superconductors offers ideal magnetic shielding, truly equipotential bus, absence of thermal electromotive forces, and high Q resonators.