Quarter-Volt output for Josephson standard

National Institute of Standards and Technology (NIST) researchers have developed the first intrinsic quantum standard for alternating current (AC) voltage, making possible more precise measurements and comparisons with existing power-detection-based AC voltage standards.

The researchers demonstrated a direct current (DC) and AC Josephson voltage standard system that produces output voltages of up to one-quarter volt. Attaining one-quarter volt permits the system to be used in making precise calibrations for the first time.

Commercial and defence standards laboratories, as well as electronic instrumentation facilities, will be able to use the new standard for precision measurements requiring accurate and stable AC voltages. The development, for example, enables meaningful measurements with thermal transfer standards. Until now, such measurements have used power ratio comparisons, although measurement uncertainties increase as frequencies change.

This latest NIST achievement of the quarter-volt output is 40 times higher than the lab's starting point of six millivolts when work began six years ago. The team, however, is striving to attain output voltages of a half volt to one volt in the next year or two. That would reduce uncertainties in AC voltage measurements by three to four orders of magnitude, similar to today's DC volt standards that are based on quantum effects.