Recovering the homogeneous absorption of inhomogeneous media. (arXiv:1904.06233v1 [quant-ph])

The resonant absorption of light by an ensemble of absorbers decreases when
the resonance is inhomogeneously broadened, as only a fraction of the ensemble
contributes to the absorption at any given optical frequency. Recovering the
lost absorption cross-section is of great importance for various applications
of light-matter interactions, particularly in quantum optics and for few-photon
nonlinearities. However, no recovery mechanism has yet been identified and
successfully demonstrated. Here, we first formulate the limit set by the
inhomogeneity on the absorption and then present a mechanism able to circumvent
this limit and fully recover the homogeneous absorption of the ensemble. We
experimentally study this mechanism using hot atomic vapor and demonstrate a
5-fold enhancement of the absorption above the inhomogeneous limit. Our scheme
relies on light shifts induced by auxiliary fields and is thus applicable to
various physical systems and inhomogeneity mechanisms.

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