Rydberg states of alkali atoms in atomic vapour as SI-traceable field probes and communications receivers

Rydberg states of alkali atoms are highly sensitive to electric fields because their electron wavefunction has a large spatial extent, leading to large polarizabilities for static fields and large transition dipole moments for time-varying fields. Over the past few years, Rydberg atoms have been used as sensitive probes for performing self-calibrated and SI-traceable electric field measurements. In this Technical Review, we introduce and examine the current state of Rydberg atom-based electrometry in room-temperature atomic vapours. We cover the fundamental principles, experimental techniques, recent advancements, and applications of this field, providing a comprehensive resource for researchers interested in utilizing Rydberg atoms for precise electric field measurements. Rydberg atoms are sensitive to radio frequency electric fields, which make them useful as sensors. This Technical Review discusses Rydberg sensors that measure the amplitude and phase of electric fields at frequencies from d.c. to THz, as well as technological applications of these sensors.