Dynamic control of photonic bandgap mediated by vacuum-induced coherence

We theoretically examine the storage and retrieval of a light pulse in a medium comprised of four-level atoms of the V − Λ-type. The two intermediate levels are probed by a weak field and vacuum-induced coherence effects lead the system to transparency. The temporal variation of the intermediate levels' splitting is used as an external parameter which allows the transfer of the impinging field to a combination of spin coherences. An auxiliary and far-detuned control field in a standing-wave configuration is used to induce a variable photonic bandgap by cross-phase modulation. It is shown that dynamic control of such a bandgap can be used to coherently manipulate the previously stored probe pulse. We use a general scheme to take into account multiwave mixing effects and solve the combined Maxwell-Bloch equations for the relevant coherences. It is shown that the system acts as an all-optical router.