The NIMT Voltage laboratory develops and maintains national standards for voltage measurement. These include primary voltage standard , Josephson Junction Voltage Standard (JJVS), which based on quantum effects. The most familiar quantum standard is the Josephson array voltage standard. For two superconductors separated by a very thin insolating layer (a so-called Josephson junction), a DC voltage difference will occur when an RF bias current is supplied. The voltage V will only depend on the frequency f of the supplied signal and on constants of nature:
where n is a tunable integer number that can be tuned using for example a DC bias current, e is the electron charge and h is Planck’s constant. This voltage is known within a relative uncertainty of 10-9, since frequency can be determined very accurately (relative uncertainty better than 10-15).
The newest voltage standards that are optimized for dc voltage measurements at NIMT, called programmable Josephson voltage standard (PJVS). It is a voltage primary standard derived from frequency and the fundamental constant of the ratio between the electron charge (e) and Planck's constant (h) that is programmable and high accurate to support frontier research in the natural sciences, including quantum metrological triangle research and redefining the unit of mass, kg (redefinition of the kilogram), and can also be developed to measure AC voltage called AC Quantum Voltmeter.
on-site JVS comparison between BIPM and NIMT in 2015
The comparison of the Josephson array voltage standards between BIPM and NIMT of the BIPM.EM-K10.b comparison protocol were applied. Option B required the BIPM to provide a reference voltage for measurement by the NIMT using its Josephson voltage standard with its own measuring device. The final results were in good agreement within the combined relative standard uncertainty of 2.6 parts in 1010 for the nominal voltage of 10 V.
Josephson Junction voltage standard : JJVS
Programmable Josephson Voltage Standard : PJVS
The PJVS has had great success generating large output voltages by biasing the Josephson junctions with 70 GHz microwave signals. A single microwave signal is input to the superconducting integrated circuit where it is divided to bias 32 or 64 different JJ arrays. This on-chip division of the microwave signal is accomplished using multiple stages of microwave dividers. Dividers with modest bandwidth are sufficient because PJVSs use a single-frequency bias.
A Group of DC Reference standards
The voltage laboratory has installed a group of voltage standard equipment. To be used as a reference standard in transferring the accuracy of DC voltage to secondary standards, such as DC standard, calibrator and digital multimeter, etc. This voltage standard group consists of 4 DC voltage standard.
