Self-Calibrating Rydberg Electrometer for Radio Frequency and Microwave Field Detection

Accurate detection and characterization of radio frequency (RF) and microwave (MW) electric fields are crucial capabilities for numerous scientific and practical applications. This dissertation describes a self-calibrating electromagnetic field sensor for measuring the amplitude and frequency spectrum of RF fields. The sensor employs Rydberg Rubidium atoms in a room temperature vapor cell and electromagnetically induced transparency (EIT) laser spectroscopy as an optical readout.

The electrometer utilizes non-resonant dressing of Rydberg atoms in combined RF and DC, low frequency (LF), or RF reference electric fields to exploit the exceptionally large field sensitivity (i.e. polarizability) of Rydberg atoms. In the presence of an unknown "signal" and known "reference" fields, the Rydberg excitation spectrum obtained through laser spectroscopy exhibits a primary Rydberg resonance feature Stark-shifted from the zero-field resonance. This primary resonance is flanked by subsidiary resonances (sidebands) whose splittings directly reflect the frequencies of the signal and reference fields.

Spectroscopic measurement of the shift of the primary Rydberg resonance, along with the ratio of the sideband to primary Rydberg resonance amplitudes, enables the determination of the spectral amplitude of the RF field. The instrument offers high sensitivity across a broad spectral range, and is not limited by a resonant or near-resonant atomic response.

Furthermore, it is self-calibrating and does not require detailed knowledge of the signal field frequency for effective operation. Measurements over a wide range of field amplitudes can be accomplished with the same instrument using Rydberg states with larger principal quantum numbers and a large reference field for weak signal fields, and lower-n Rydberg states and direct AC Stark shift measurements with no reference for the strongest signal fields. Characterization of higher frequency fields (e.g. in the microwave regime) can be accomplished, without requiring rapid laser scanning over a wide frequency range, through the use of low-n Rydberg states and a high frequency reference.

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