RF electric field sensing with atoms in superpositions of Rydberg states with oppositely oriented static electric dipole moments

The large static electric dipole moments (>1000 e a₀) associated with high Rydberg states in atoms lead to strong linear Stark energy shifts, and high sensitivity to dc and radio frequency electric fields. Atoms in coherent superpositions of pairs of these states with oppositely oriented dipole moments can be exploited to implement quantum sensors with very high electric field sensitivity. However, the direct preparation of such superposition states, for example, using pulses of resonant microwave radiation, is challenging because of the near-zero spatial overlap of their electronic wave functions, which leads to small electric dipole moments for transitions between them. Here, we overcome this challenge by preparing (helium) atoms in superpositions of │ns〉 Rydberg states with pulses of microwave radiation, and allow these to coherently evolve into superpositions of states with strong oppositely oriented induced static electric dipole moments through the application of carefully controlled time-varying electric fields. By appropriately tailoring these time-varying fields, the atoms in these superposition states have been exploited to measure the phase and amplitude of a single-cycle 5 MHz electric field pulse with an amplitude ~100 μV/cm. By adjusting the time-varying electric field to manipulate these superposition states, this Rydberg atom electrometer can be tuned to allow selective detection of more complex waveforms. The operation and characterisation of this coherent Rydberg-atom quantum sensor will be presented.