Remote Quantum Voltage Standard Comparison for PPM-Level Calibration of High-Voltage Measurement Systems

The metrological assurance of high-voltage measurements is a cornerstone for research, power transmission, and advanced industrial applications such as particle accelerators, X-ray generators, and materials testing. Achieving and verifying accuracy at the parts-per-million (PPM) level presents a formidable challenge, particularly when calibrating systems across different geographical locations. This article explores the application of remote quantum voltage standard comparison as a paradigm-shifting methodology for the ultra-precise calibration of high-voltage DC and AC measurement systems. Traditional high-voltage calibration relies on the transport of physical reference dividers or standards to a national metrology institute (NMI), a process that is time-consuming, expensive, and introduces risks associated with transportation shocks and environmental drifts. The concept of remote comparison utilizing quantum standards—specifically the Josephson Arbitrary Waveform Synthesizer (JAWS) or Josephson Voltage Standards (JVS) based on the internationally fixed Josephson constant—offers a solution. These standards generate intrinsically accurate voltages traceable to fundamental physical constants, not to artifact standards. For high-voltage applications, the quantum standard itself operates at low voltage (typically up to 10 V). Its unparalleled accuracy is transferred to high-voltage ranges via the remote calibration of the scale factors of ultra-stable high-voltage dividers or measurement amplifiers. The process involves a sophisticated comparison scheme. At a primary laboratory, a quantum voltage standard is used to characterize a high-precision transfer standard, such as a temperature-controlled resistive voltage divider with a known stability in the sub-PPM range over specified time intervals. This characterized divider is then installed at the remote user's site. Subsequently, a remote comparison is executed. This is not a simple data transmission but a coordinated measurement campaign where both laboratories—the NMI and the user's facility—simultaneously measure a stable, transportable voltage source (which could be a high-precision calibrator or a stable high-voltage supply) against their local standards (the quantum standard at the NMI and the pre-characterized divider at the user's site). The key is the use of a GPS-disciplined or similar time-reference system to synchronize measurements and to employ advanced data analysis techniques to account for signal propagation delays and noise. The measurement data, consisting of voltage ratio readings and timestamps, are exchanged and analyzed. By comparing the results obtained from the user's divider (now acting as a remote reference) with the results virtually linked back to the quantum standard, the scale factor and linearity of the user's entire high-voltage measurement chain—including the divider and any subsequent digital voltmeters—can be validated or calibrated at the PPM level, all without moving the bulky high-voltage equipment. This approach decouples the need for the user to possess a quantum standard. It instead leverages a pre-calibrated, stable artifact as a transfer intermediary, whose fidelity is maintained and periodically re-verified through remote quantum comparisons. The implications for high-voltage power supply applications are profound. Manufacturers and users of high-precision high-voltage sources for fields like dielectric spectroscopy, electron microscopy, or aerospace component testing can now establish reliable, internationally traceable calibration with unprecedented accuracy and minimal downtime. It ensures that a voltage rated at 100 kV in one laboratory is truly equivalent to the same nominal value in another, fostering confidence in comparative research and quality assurance in global supply chains. The technical hurdles involve ensuring the long-term stability of the transfer standards, developing secure and robust data communication and analysis protocols, and establishing internationally agreed-upon procedures for such remote quantum comparisons, which are now actively being developed within metrology consortiums worldwide.