Rydberg atom-based electrometry enables traceable electric field measurements with high sensitivity over a large frequency range, from gigahertz to terahertz. Such measurements are particularly useful for the calibration of radio frequency and terahertz devices, as well as other applications like near field imaging of electric fields. We utilize frequency modulated spectroscopy with active control of residual amplitude modulation to improve the signal to noise ratio of the optical readout of Rydberg atom-based radio frequency electrometry.Matched filtering of the signal is also implemented. Although we have reached similarly, high sensitivity with other read-out methods, frequency modulated spectroscopy is advantageous because it is well-suited for building a compact, portable sensor. In the current experiment, ∼3 µV cm −1 Hz −1/2 sensitivity is achieved and is found to be photon shot noise limited.

We calculate pair potential curves for interacting Rydberg atoms in a constant electric field and use them to determine the effective C 3 dipole-dipole and C 6 van der Waals coefficients. We compare the C 3 and C 6 with experiments where the angle of a polarizing electric field is varied with respect to the axis of a quasi-1-dimensional trap at ultracold temperatures. The dipoles produced via polarization of the atoms have an angular dependent dipole-dipole interaction. We focus on the interaction potential of two rubidium Rydberg atoms in 50S 1/2 states in the blockade regime.For internuclear distances close to the blockade radius, R bl ≈ 4 − 6 µm, molecular calculations are in much better agreement with experimental results than those based on the properties of single atoms and independent calculations of C 3 and C 6 which were used to analyze the original experiment. We find that the calculated C 6 coefficient is within 8% of the experimental value while the C 3 coefficient is within 20% of the experimental value.