The creation of non-classical states of light is an interesting problem, that we solve sending atoms through an optical cavity. We show that it is possible to add or subtract many photons from a cavity field by interacting it resonantly with a two-level atom. The atom, after entangling with the field inside the cavity and exiting it, may be measured in one of the Schmidt states, producing a multiphoton process (in the sense that can add or annihilate more photons than a single transition allows), i.e. adding or subtracting several photons from the cavity field. By plotting the quadratures and the Husimi Q-function, we also show that the non-classical state produced by such measurements is a squeezed state.
Resonant field enhancement in an optical cavity is a promising pathway towards realizing optical nonlinearities at the few-photon level. This quest is hampered by inevitable narrowing of the resonant linewidth as the cavity finesse is increased, which necessitates striking a compromise between the magnitude of the field enhancement and the bandwidth over which it is harnessed. This difficulty is exacerbated for broadband entangled-photon pairs, which are typically frequency-anticorrelated, so that the two photons cannot be simultaneously admitted to a cavity except when the degenerate wavelength coincides with a cavity resonance. Here we show that introducing judicious angular dispersion into single-photon and entangled-photon states before incidence on a planar Fabry-P{é}rot (FP) cavity renders these non-classical fields omni-resonant: the entire spectrum is coupled to a single longitudinal cavity mode. Making use of a planar FP cavity of finesse
≈100, resonant linewidth
≈0.3~nm, and free spectral range
≈22~nm in the near-infrared, we couple single-photon states and frequency-anticorrelated entangled-photon states of 20-nm bandwidth to a broadband achromatic resonance associated with a single underlying narrowband longitudinal FP-cavity mode -- thereby preserving the entangled spectral structure. In general, pre-conditioning the optical field by introducing angular dispersion enables coupling non-classical states of light to a single longitudinal cavity mode, even if the field bandwidth far exceeds the resonant linewidth, or even exceeds the cavity free-spectral-range. These results pave the way to broadband resonant interactions with non-classical states of light in photon-starved applications.