Cavity-Controlled High Harmonic Generation

Employing non-Hermitian Floquet theory, the strong-field process of high harmonic (HH) generation by a classical continuous-wave field irradiating ground-state atom is discovered to be controllable by placing the irradiated atom inside a single-mode quantum cavity initiated even with a single photon. Judicious cavity coupling of cavity-free photo-induced atomic Floquet states forms polaritonic Floquet states that generate side harmonics around the (standard no-cavity) odd harmonics. The different possible cavity-controlled HH spectra, including also the ones resulting from several cavities in a row, enable attosecond-pulse sequences different from the one produced without a cavity. Moreover, the present study sets the framework and opens the way for further cavity control over the HH generation process as well as over other strong-field processes