AC-DC difference measurements relative to Josephson generated voltages

In an extension from their original use as references for measuring dc voltage, Josephson generated voltages from programmable arrays have been employed to measure waveforms differentially. In this paper, the alternative of using these Josephson voltages as a reference for ac-dc difference measurements using thermal converters and sampling techniques is presented.

Introduction

Programmable Josephson arrays [1] have made possible the deterministic generation of quantized voltages at a defined point in time. Combined with a computer controlled bias source in the Josephson Waveform Synthesizer (JWS) and additional synchronous current sources, they have been used to measure ac-dc differences using Thermal Converters (TCs) [2]–[4]. The JWS can also be used to provide a time-dependent reference voltage for differential measurements using sampling techniques, as in the ac-Quantum voltmeter [5], [6]. Or, as in this paper, for TC measurements. At dc, the procedure basically follows best practice recommendations for measurements involving a Josephson array. For ac, the JWS can either be used as a reference for a measurement with a lock-in amplifier [7], [8] or as presented in this paper. Both methods are compared and shown to agree to a very low uncertainty at low frequencies in [9].