Rydberg Radio-Frequency Electrometry with High-Angular-Momentum States

This thesis details a two-photon method for coupling high–orbital-angular-momentum Rydberg (highly-excited) states in a thermal caesium vapour, allowing broadband radio frequency (rf) sensing and precision spectroscopy. Using a sequence of rf driven transitions, whose energy spacings decrease significantly with increasing angular momentum, we demonstrate a Rydberg atom receiver capable of simultaneous detection of fields ranging from 128 MHz to 0.61 THz. The optical response to multiple simultaneous rf fields is reproduced theoretically, and we show experimentally that amplitude-modulated signals across these widely separated carrier frequencies can be demodulated concurrently. The same scheme enables rf and terahertz (THz) spectroscopy of states with 15 ≤ n ≤ 22 and 2 ≤ ℓ ≤ 8. Through a global fit to measured transition frequencies, we extract a complete, independent set of quantum defects in 133Cs and determine the ionic-core dipole and quadrupole polarisabilities of Cs+, finding αd = 15.729(18) a30 and αq = 76.3(1.9) a50 respectively. These results allow prediction of all Cs Rydberg energy levels with uncertainties of 1 MHz or less. Finally, we analyse the fundamental and technical noise limits of EIT-based Rydberg-atom sensors, separating the contributions of photon shot noise, laser technical noise, and others. This establishes the dominant factors currently limiting sensitivity in warm-vapour Rydberg receivers and provides guidance for future direction. Together, these results further develop and demonstrate the strengths of Rydberg atoms as electric field sensors while simultaneously improving the spectroscopic data required for accurate modelling of many atomic physics experiments.