No, they use a conventional antenna, hence the title "Waveguide-Coupled Rydberg Spectrum Analyzer". The Rydberg atoms essentially serve as an active frequency m

No, they use a conventional antenna, hence the title "Waveguide-Coupled Rydberg Spectrum Analyzer". The Rydberg atoms essentially serve as an active frequency mixer that produces the difference frequency between the RF input and a local oscillator. This is how conventional spectrum analyzers work, except that their mixers are based on semiconductors.