James W. Schmidt, R Gavioso, E May, Michael R. Moldover
Using a quasi-spherical, microwave cavity resonator, we measured the refractive index of helium to deduce its molar polarizability Aε in the limit of zero density. We obtained (Aε,meas - Aε,theory)/Aε = (-1.8plus or minus} 8.4)× 10-6, where the standard uncertainty (8.4 ppm) is factor of 3.6 smaller than that of the best previous measurement. If the theoretical value of Ae is accepted, these data determine a value for the Boltzmann constant that is only (1.8 plus or minus} 8.4) ppm larger than the accepted value. Our techniques will enable a helium-based pressure standard and measurements of thermodynamic temperatures.
Physical Review Letters
Boltzmann constant, dielectric constant, fundamental constant, helium, index of refraction, microwave resonator, polarizability, pressure standard, temperature standard