PTB–INRIM comparison of novel digital impedance bridges with graphene impedance quantum standards

Abstract

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.

Development and implementation of an automated four-terminal-pair Josephson impedance bridge

“…To check if the bridge is operating as expected, we verified if the product of these three measurements (R H /R 12.9 kΩ ) × (R 12.9 kΩ /Z C2 ) × (Z C2 /R H ) is 1. In our measurements, the product deviated from the expected value by 36 nΩ Ω −1 , with an associated standard uncertainty of 16 nΩ Ω −1 [14]. The triangle check was repeated within the same week, resulting in a slight difference of 1 nΩ Ω −1 compared to the initial check.…”

“…This analysis assessed the charge carrier density and mobility. The charge carrier density was p = 5.5 × 10 10 cm −2 and carrier mobility was on the level of µ = 5900 cm 2 V −1 s. The DC characterization displayed the resistance plateau between −2 T to −7 T, with the lowest longitudinal resistivity observed at −5 T. Detailed information on the characterization measurements for this device can be found in [14].…”

“…Additional research involved a collaboration with the Istituto Nazionale di Ricerca Metrologica (INRIM) and the Politecnico di Torino (POLITO), Italy, resulting in an extensive assessment of the 4TP Josephson impedance bridge, as reported in Marzano et al [14]. We performed on-site comparisons between PTB's Josephson impedance bridge and INRIM-POLITO's digital impedance bridge.…”

Josephson voltage standards as toolkit for precision metrological applications at PTB

“…Every deviation of the result from 1 gives a hint to unaccounted systematic uncertainties. For the Josephson impedance bridge this deviation is 2 parts in 10 8 after subtracting the combined uncertainty of 1.6 parts in 10 8 (k = 1) and is currently under investigation (Marzano et al 2022).…”

“…Recently the onsite comparison of two digital impedance bridges combined with a graphene quantum Hall standard has been published (Marzano et al 2022). One bridge the INRIM-POLITO digital impedance bridge using a polyphase digital sinusoidal waveform generator (Marzano et al 2020).…”