This paper introduces a four-terminal-pair impedance bridge based on pulse-driven Josephson junctions arrays which is designed to link any kind of impedance to the quantized Hall resistance. The unique features of the quantized Hall resistance in a multiple series connection allows to dispense a combining network and leads to a compact and simple design of the whole setup. Moreover, the low noise of a quantized Hall resistance reduces the measurement time compared to resistance standards at room temperature which is essential for the characterization of quantum Hall devices in the AC regime. A first measurement campaign confirmed the expected low noise of 1.82  n V / H z for a link to a 10 nF capacitance standard. The repeatability of the bridge was found to be few parts in 108. Capacitance and resistance standards were measured at 1233.15 Hz against graphene based quantum Hall resistance devices.

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This paper describes an onsite comparison of two different digital impedance bridges when performing measurements on a quantum Hall resistance standard with the purpose of realizing the SI unit of capacitance, the farad. In the EMPIR Joint Research Project 18SIB07 GIQS, graphene impedance quantum standards, the Physikalisch-Technische Bundesanstalt (PTB), Germany, developed a Josephson impedance bridge, and the Istituto Nazionale di Ricerca Metrologica (INRIM) and the Politecnico di Torino (POLITO), Italy, developed an electronic digital impedance bridge. The former is based on Josephson waveform generators and the latter on an electronic waveform synthesizer. The INRIM-POLITO impedance bridge was moved to PTB and the two bridges were compared by measuring both temperature-controlled standards and a graphene AC quantized Hall resistance standard. The uncertainties for the calibration of 10 nF capacitance standards at 1233 Hz are within 1 × 10-8 for the PTB’s bridge and around 1 × 10-7 for the INRIM-POLITO’s bridge. The comparison mutually validates the two bridges within the combined uncertainty. The result confirms that digital impedance bridges allow the realization of the SI farad from the quantized Hall resistance with uncertainties comparable with the best calibration capabilities of the BIPM and the major National Metrology Institutes.

The Josephson arbitrary waveform synthesizer is a quantum-based voltage source that can generate arbitrary waveforms with quantum accuracy. However, these state-of-the-art performances are drastically decreased by the wiring connecting the source to the device under test. This wiring introduces deviations from the Josephson voltage which scale quadratically with frequency. This paper describes a load compensation bridge that fully compensates the load of the Josephson arbitrary waveform synthesizer by the input impedance of the device under test and completely suppresses the frequency dependence up to a frequency of 80 kHz with an overall uncertainty of 2.8 V V−1.

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