Degenerate Two-Photon Rydberg Atom Voltage Reference

Abstract

We implement a DC voltage reference by measuring Stark shifts of cesium Rydberg atoms in a vapor cell. Cesium atoms are excited from the ground state to the 15s state via a degenerate two-photon transition that provides a narrow, Doppler free line. The 15s state experiences a scalar, quadratic stark shift which is used to measure the voltage across a parallel plate capacitor integrated into the vapor cell. We demonstrate a sensitivity of $82\text{mV}/\sqrt{\text{Hz}}$ at a bias voltage of 100 V. The device could be adapted for even larger voltages by increasing the plate spacing or using a lower energy state.

FIG. 1.

a) Energy level diagram of Cs and the degenerate two-photon transition to the 15s state at 656 nm, which is detuned by about 100 THz from the nearest intermediate level. b) Schematic of experiment. ECDL: external cavity diode laser, ISO: isolator, HWP: half wave plate, DL: diode laser, TA: tapered amplifier, SPF: short pass filter, PMT: photomultiplier tube, TIA: transimpedance amplifier. c) Drawing of glass-blown Cs vapor electrode cell with internal, stainless steel electrodes.

FIG. 2.

a) Fluorescence signal versus laser frequency at various electrode voltages (dashed line shows quadratic fit to peak centers). b) Stark shift measured using beat note with frequency comb (left axis) and transition linewidths (right axis). The larger 8 MHz linewidth at 0 V bias appeared to be an anomoly of this particular dataset. Other measurements at 0 V resulted in linewidths closer to 5.7 MHz. The fit to the measured shifts takes the form $f_s={\alpha }_1{V}^2$ and the fit to the measured widths takes the form $\gamma ={\alpha }_2{V}^2+\beta$. Residuals of quadratic fit to measured Stark shifts are shown below

FIG. 3.

a) Fluorescence signal from electrode cell (A) and reference cell (B) at 100 V. 100 scans were averaged together for this plot. b) Measured sensitivity of the voltage reference. The signal at 40 Hz is due to the $1V_{p-p}$ voltage applied to the electrodes. c) Voltage Allan deviation as a function of averaging time with 100 V bias (error bars represent 68 % confidence intervals).