Quantum sensing of weak GHz frequency fields – towards a microwave single photon detector?
Dr. Friedemann Reinhard (Walter Schottky Institut der TU München)

Solid state qubits, such as the Nitrogen-Vacancy (NV) center in diamond, have become powerful sensors for nanoscale magnetic and electric fields. A major key for their success have been dynamical decoupling protocols, which efficiently pick up tiny alternating (AC) signals.
Currently, those methods are limited to signal frequencies up to several MHz.
I will present a novel dynamical decoupling protocol specifically designed to detect weak fields close to the NV's transition frequency (~2 GHz).
It exploits a quantum-optical effect, the Mollow triplet splitting of a strongly driven two-level system. We microscopically understand this effect as a pulsed dynamical decoupling protocol and find that it enables sensitive detection of fields close to the driven transition.
Employing a nitrogen-vacancy center, we detect GHz microwave fields with a signal strength (Rabi frequency) below the current detection limit, which is set by the center’s spectral linewidth 1/T2*.

I will speculate on possible applications, in particular spin-phonon coupling and detection of single microwave photons in superconducting circuits.