  We investigate the Stark shift in Rydberg rubidium atoms through
electromagnetically induced transparency for the measurement of direct current
(dc) and 60~Hz alternating current (ac) voltages. This technique has direct
applications to atom-based measurements of dc and ac voltage and the
calibration of voltage instrumentation. We present experimental results for
different atomic states that allow for dc and ac voltage measurements ranging
from 0~V to 12~V. A Rydberg atom-based voltage standard could become an
alternative calibration method with more favorable size, weight, power
consumption, and cost compared to the more precise Josephson voltage standard.
In this study, we also demonstrate how the voltage measurements can be utilized
to determine the atomic polarizability for the Rydberg states. The Rydberg
atom-based voltage measurement technology would become a complimentary method
for dissemination of the voltage scale directly to the end user.
