Narrow-band filter for quantum light

Atom-photon interaction promises to be a fundamental resource for applications like quantum computations. For an efficient interaction between light and atoms, the bandwidth of the light should match the natural linewidth of the atom transition to address, 6 MHz in the case of the Di line of rubidium. Cavity-enhanced down-conversion (CEDC) produces bright narrow-band quantum light with suitable linewidth but multimode in frequency. This requires the use of one or more filter cavities. This paper investigates a narrow-band filter which can be used for filtering the spectral mode of interest with a high extinction ratio for the other modes. Combined with a CEDC, this filter provides light for optimal interaction with rubidium atoms.