Optimal Atomic Quantum Sensing using EIT Readout

Abstract

Quantum sensors offer the capability to reach unprecedented precision by utilizing large quantities of identical atoms and resolving signals down to the standard quantum limit (SQL) governed by individual wave-function collapse. The ability to achieve quantum-limited sensing depends on the interrogation method. We derive the optimum sensitivity of a three-level quantum sensor based on electromagnetically-induced transparency (EIT) or, more generally, coherent spectroscopy, and compare this to the SQL while allowing for strong probing fields, thermal broadening, and large optical depth. We derive the optimal laser intensities and optical depth, providing specific guidelines for sensitive operation under common experimental conditions. Clear boundaries of performance are established, revealing that ladder-EIT can not achieve the SQL due to unavoidable associated absorption loss. This work is particularly relevant for emerging electric-field sensors that rely on EIT spectroscopy of Rydberg states.