Span shift and extension of quantum microwave electrometry with Rydberg atoms dressed by an auxiliary microwave field

The Rydberg electromagnetically induced transparency (EIT)--Autler Townes (AT) splitting proportional to the target microwave electric field strength is an atom-based primary traceable standard in microwave electrometry. The minimum detected microwave electric field is limited when the EIT-AT splitting is indistinguishable. We design a method for auxiliary microwave-dressed Rydberg atoms that extends the electrometric span. We theoretically and experimentally show that the low bound of the direct SI-traceable microwave electric field is extended by two orders of magnitude, which is from several mV/cm to $\ensuremath{\mu}\mathrm{V}/\mathrm{cm}$ in a room-temperate Rb cell with a modest setup.