Brian Josephson’s discovery in 1962 of the quantum behavior of superconducting Josephson junctions enabled a revolution in precision voltage measurement, where quantum-based standards that are intrinsically accurate replaced electrochemical battery standards whose behavior depends on environmental conditions. I will describe the major technological advances in junction fabrication, superconducting integrated circuits, instrumentation, and measurement techniques that led to the present generation of practical dc and ac voltage standard systems. Quantum-based 10 V programmable Josephson voltage standards and 4 V rms Josephson arbitrary waveform synthesizer signals at audio frequencies are used in electrical metrology, primarily for calibration of dc and ac voltage, ac power, and impedance. They were also key instruments in precision measurements of “the kg” and the triple point of water. The results of these measurements contributed to new values of the Planck and Boltzmann constants. These became exact “defined” values under the 2019 redefinition of the international system of units (SI) so that the “redefined SI” is based on physical constants of nature and not on artifacts. Finally, I will describe new devices that synthesize quantum-based signals at radio frequencies that are aimed at improving radio-frequency metrology for spectrum sharing and communications and at generating repeatable signals for controlling qubits.

Figure: NIST Josephson Arbitrary Waveform Synthesizer Standard Reference Instrument.

References:
1. S. P. Benz, “Synthesizing accurate voltages with superconducting quantum-based standards,” IEEE Instr. Meas. Magazine, June 2010, pp. 8-13, doi: 10.1109/MIM.2010.5475160.

2. A. Rüfenacht, et al., "Impact of the New Generation of Josephson Voltage Standards in ac and dc Electric Metrology," accepted to Metrologia vol. 55, no. 5, pp. S152–S173, Aug 24, 2018 doi: 10.1088/1681-7575/aad41a.

3. N. E. Flowers-Jacobs, et al., “Calibration of an AC Voltage Source Using a Josephson Arbitrary Waveform Synthesizer at 4 V,” 32st Conference on Precision Electromagnetic Measurements (CPEM 2020) Digest, Aug. 24 - 28, 2020, Denver, CO. doi: 10.1109/CPEM49742.2020.9191787.

4. J. A. Brevik, et al., “A Cryogenic Calibration of a Quantum-Based RF Source,” 2020 95th ARFTG Microwave Measurement Conference (ARFTG) Digest, Aug. 4-6, 2020, Los Angeles, CA, pp. 1-4, doi: 10.1109/ARFTG47271.2020.9241378.

5. F Overney, et al., “Dual Josephson impedance bridge: towards a universal bridge for impedance metrology,” Metrologia, Vol. 57, Num. 6, pp. 1-17, Oct. 22, 2020, doi: 10.1088/1681-7575/ab948d.

6. A. J. Sirois, et al., “Josephson Microwave Sources Applied to Quantum Information Systems”, IEEE Trans. Quant. Eng., vol. 1, pp. 1-7, 18 Dec. 2020, Art no. 6002807, doi: 10.1109/TQE.2020.3045682.

7. M. A. Castellanos-Beltran, et al., “Single-Flux-Quantum Multiplier Circuits for Synthesizing Gigahertz Waveforms with Quantum-Based Accuracy”, IEEE Trans. Appl. Supercond., vol. 31, no. 3, pp. 1400109-9, 3 Feb 2021, doi: 10.1109/TASC.2021.3057013.

Keywords: Josephson junction, voltage standard, metrology, quantum