  We realize a non-invasive electrometer based on state engineering in a
Rydberg hydrogenic manifold. A quantum interference process involving states
with very different dipoles measures directly the time correlation of a
stochastic electric field, with a 200~ns time resolution and with a
$83.2\pm1.4$~mV/m single-atom sensitivity, beyond the Standard Quantum Limit in
this context. This quantum-enabled correlation electrometer opens the way to
applications in mesoscopic physics, e.g. for the study of individual charge
transits in nano-structures.
