The Impact of Thermal Fields on Rydberg Atom Radio Frequency Sensors

Abstract

Rydberg atom radio frequency sensors are unique in a number of ways, including possessing extraordinary carrier bandwidth, self-calibration and accuracy. In this paper, we examine the impact of thermal radiation on Rydberg atom sensors. Antennas are limited by their thermal background, while Rydberg atom sensors are coherent sensors. Incoherent thermal radiation does not limit Rydberg atom sensors in the same way as an antenna. The primary consequence of a thermal radiation field on Rydberg atom sensors is to decrease their coherence, as the decay rates of the Rydberg states used for sensing the radio frequency field are increased due to the thermal field, i.e. blackbody, modification of the atomic decay rates. Thermal and coherent field excitation are fundamentally different in that thermal fields produce statistically independent excitations with well-defined frequency, polarization, and propagation direction, while coherent states are coherent superpositions of photon number states. Consequently, thermal fields do not contribute to the coherences of the density matrix that are used for Rydberg atom sensing, except for damping them.

Figures (3)

• Figure 1: (a) Experimental setup. (b) Energy level diagram employed. The probe laser was locked to the Cs $|6S_{1/2},F=4\rangle$ to $|6P_{3/2},F=5\rangle$ transition. The coupling laser was tuned to the $|6P_{3/2},F=5\rangle$ to $30D_{5/2}$ transition while the RF field drove the $30D_{5/2}$ to $28F_{7/2}$ transition. (c) Time-domain trace of the lock-in amplifier output signal where $I^T_{\rm E}$ and $I^T_{\rm RF}$ are the EIT transmission intensities with and without RF, respectively.
• Figure 2: (a) $\Delta \beta_{\rm E}$ as a function of $\Delta T_{\rm BB}=T_{\rm BB}-T_{\rm room}$, where $T_{\rm BB}$ is the BBR temperature and $T_{\rm room}$ is the room temperature. (b) $\Delta \beta_{\rm RF}$ as a function of $\Delta T_{\rm BB}=T_{\rm BB}-T_{\rm room}$. Each data point is the average over 160 measurements. The error bars are the standard deviation at each measurement point. The error on the temperature axis are $\pm0.4~\rm K$, too small to be visible. The dashed lines are the numerically calculated results.
• Figure 3: Relative change in absorption coefficient, $\beta_{\rm E}$, as a function of the coupling laser Rabi frequencies at $T_{\rm BB}= 773.15$ K. The inset shows the relative change in EIT amplitude, $I_{\rm E}$, as a function of coupling laser Rabi frequency. The largest change in EIT amplitude happens when $\Omega_{\rm C}=4.5 \rm MHz$, as indicated by the red dashed line in the inset. The error bars in both plots are reflective of the standard deviation of each measurement point.