Use a quantum relationship as the reference
NIST’s Quantum Voltage Project describes superconducting devices called Josephson junctions. Driven by a microwave signal, they produce an exactly calculable voltage tied to the signal’s frequency and fundamental constants. This supplies a physical reference for electrical measurement. It is an established metrology technique, not a new quantum-computing announcement. [1]
- Microwave frequency drives junctions
- Junction array supplies a voltage reference
- Compare the meter with that reference
A reference helps check another instrument
NIST’s programmable system generates direct-current voltages and can calibrate other voltage references and digital voltmeters. Comparing a meter with a known reference helps evaluate its response across its range. The project uses specialized superconducting equipment with cooling; the quantum relationship is implemented by a complete laboratory instrument. [1] [2]
Changing voltage adds another question
NIST distinguishes steady voltage levels from the transitions between them. Its instrument description says stepwise waveforms do not automatically inherit quantum accuracy because the transitions depend on the applied bias. Generating accurate changing signals therefore requires appropriate techniques, rather than assuming that accurate steps settle the whole waveform. [2]
Go a little deeper
Optional reading · about 1 more minute
A perfect relationship is not a perfect measurement
The instrument page gives calibration uncertainty that depends on the measuring equipment and noise in the reference being tested. A fundamental relationship can anchor a standard while the practical comparison still has uncertainty. That distinction is part of using the instrument, not a contradiction. [2]
What the page dates mean
Our interpretation: NIST updated the project page on September 22 and the instrument page on September 8, 2026. Those page dates are not the invention dates of the Josephson effect. This story explains how the reference works and where a reader should look for its practical limits. [1] [2]
Original sources
Attributed synthesis, not original reporting. Examples labeled hypothetical or illustrative are explanatory. Reviewing a source does not independently validate its findings.
- NIST: Quantum Voltage Project ↗
Project description created November 19, 2008; updated September 22, 2026. Mechanism, cooling and calibration use read September 25.
- NIST: Programmable Josephson Voltage Standard ↗
Instrument page created September 28, 2016; updated September 8, 2026. DC, waveform-transition and calibration limitations read September 25; no purchase recommendation.