Optimal atomic quantum sensing using electromagnetically-induced-transparency readout

Quantum sensors offer the capability to reach unprecedented precision by operating at standard quantum limit (SQL) or beyond using entanglement. But an emerging class of that use Rydberg electromagnetically induced transparency (EIT) detect rf electric fields have yet SQL. In this work we prove discrepancy is due fundamental limitations in EIT probing mechanism. We derive optimum sensitivity a three-level sensor based on EIT, more generally coherent spectroscopy, and compare apply minimal set assumptions, while allowing strong fields, thermal broadening, large optical depth. optimal laser intensities depth, providing specific guidelines for sensitive operation under common experimental conditions. Clear boundaries performance are established, revealing ladder-EIT cannot achieve SQL unavoidable absorption loss. The results may be applied any EIT-based sensor, but particularly emphasize our results' importance growing field sensing.