Graphene quantum Hall devices demonstrate robust integer quantum Hall effect allowing for their use as quantum Hall resistance standards for the realization of the ohm under relaxed experimental conditions. At the National Institute of Standards and Technology (NIST), we have fabricated multiple graphene quantum Hall devices, with notable improvements in their operational parameters such as onset magnetic flux density, temperature, and biasing current. This work describes improvements in graphene quantum Hall standard realization at NIST.
With a new current source, a vertical-laser alignment system, and some other improvements in recent years, the relative standard uncertainty of NIM-2 was improved to around 3E-8 when a 1 kg mass is calibrated. In 2024, NIM participated in the third key comparison of kilogram realizations. At the same time, a compact joule balance is in design to meet the requirement of the calibration laboratory and industry in the future. An integrated mechanism of force measurement and guidance, a compact flux linkage measurement unit are in development, a small magnet and a vacuum mass transfer apparatus are in construction.
We realized a 100 Ω national reference standard using an ensemble of ultra-stable metal-foil standard resistors for the customer calibrations in NMIJ. The average of the ensemble of 100 Ω resistors is calibrated twice a year based on the quantized Hall resistance (QHR) using the cryogenic current comparator (CCC) bridge, and the predicted value of the ensemble has been used for the customer calibrations except for the direct calibration service using the QHR and the CCC. The ensemble of 100 Ω resistors shows stable resistance behavior, and the drift rate is 2.6 nΩ/Ω per year, and the temperature coefficients are α23 = 0.4 (nΩ/Ω)/K and β = 5.5 (nΩ/Ω)/K2. We had disseminated the resistance standards using the wire-wound 1 Ω standard resistors as the reference standards for more than 20 years, but the characteristics of the 100 Ω resistors are much better than those of the 1 Ω resistors, we migrated to the 100 Ω resistors on October 30, 2024.
Interest in the detection of extremely low voltages at the nanovolt level has been increasing. This paper presents the corresponding method for measuring below 10 nV using a differential dual-channel Josephson voltage standard (DJVS). A detailed analysis, focusing on the compensation method employed to suppress the inherent offset of the system, is presented on its impact on uncertainty. Subsequently, Allan variance analysis is utilized to characterize the system stability, enabling designing of the proper measurement routine to further reduce uncertainty via statistical averaging. Experimental results demonstrate that for a typical voltage of 2 nV, the measured value deviates from the nominal value by 0.2 nV, with an uncertainty of approximately 1 nV, nearly the fundamental measurement limit imposed by the noise floor of commercial nanovoltmeters. In addition, as a step toward establishing a practical DJVS dissemination, a domestically developed DC source capable of generating microvolt-level voltages was calibrated by the DJVS.
This paper presents a novel modular architecture for cutting-edge scientific instruments, Integrated Precision Measurement Architecture (IPMA). While retaining the advantages of modular platforms, this architecture adopts a unique design that can significantly improve the performance. Applications in electromagnetic measurement instruments has improved the measurement uncertainty to the level of 10-7~10-5, making precision electromagnetic measurements on modular instruments feasible.
