How to trap photons? Storing single-photon quantum states in collective atomic excitations

We show that it is possible to 'store' quantum states of single-photon fiel ds by mapping them onto collective meta-stable states of an optically dense , coherently driven medium inside an optical resonator. An adiabatic techni que is suggested which allows to transfer non-classical. correlations from traveling-wave single-photon wave-packets into atomic states and vise versa with nearly 100% efficiency. In contrast to previous approaches involving single atoms, the present technique does not require the strong coupling re gime corresponding to high-Q micro-cavities. Instead, intracavity electroma gnetically Induced Transparency is used to achieve a strong coupling betwee n the cavity mode and the atoms. (C) 2000 Elsevier Science B.V. All rights reserved.