Progress on accurate measurement of the Planck constant: watt balance and counting atoms

TL;DR

This paper reviews recent progress in measuring the Planck constant using watt balance and atom counting methods, highlighting improvements and future prospects for redefining SI units.

Contribution

It provides a comprehensive overview of the principles, recent advancements, and future directions in the precise measurement of the Planck constant at national metrology institutes.

Findings

Measurement accuracy has reached several parts in 10^8.

Progress in watt balance and atom counting methods has improved precision.

Future improvements could enable a revised physical constant system.

Abstract

The Planck constant $h$ is one of the most significant constants in quantum physics. Recently, the precision measurement of the numeral value of $h$ has been a hot issue due to its important role in establishment for both a new SI and a revised fundamental physical constant system. Up to date, two approaches, the watt balance and counting atoms, have been employed to determine the Planck constant at a level of several parts in $10^8$. In this paper, the principle and progress on precision measurement of the Planck constant using watt balance and counting atoms at national metrology institutes are reviewed. Further improvements for the Planck constant determination and possible developments of a revised physical constant system in future are discussed.