An external optical micro-cavity strongly coupled to optical centers for efficient single-photon sources
We present experimental and theoretical studies of a hemispherical, high-solid-angle external optical micro-cavity strongly coupled to nanoscale optical centers for cavity-quantum electrodynamics (QED) strong coupling and efficient single-photon sources. Implementations of single-photon sources based on various optical centers have been reported in the last three decades. The need for efficient single-photon sources, however, is still a major challenge in the context of quantum information processing. In order to efficiently produce single photons single optical centers are coupled to a resonant high-finesse optical micro-cavity. A cavity can channel the spontaneously emitted photons into a well-defined spatial mode and in a desired direction to improve the overall efficiency, and can alter the spectral width of the emission. It can also provide an environment where dissipative mechanisms are overcome so that a pure-quantum-state emission takes place. We engineered a hemispherical optical micro-cavity that is comprised of a planar distributed Bragg reflector (DBR) mirror, and a concave dielectric mirror having a radius of curvature 60 μm. Nanoscale semiconductor optical centers (quantum dots) are placed at the cavity mode waist at the planar mirror and are located at an antinode of the cavity field to maximize the coherent interaction rate. The three-dimensional scannable optical cavity allows both spatial and spectral selection to ensure addressing single optical centers. This unique micro-cavity design will potentially enable reaching the cavity-QED strong-coupling regime and realize the deterministic production of single photons. This cavity can also be operated with a standard planar dielectric mirror replacing the semiconductor DBR mirror. Such an all-dielectric cavity may find uses in atomic cavity-QED or cold-atom studies. We formulated a theory of single-photon emission in the cavity-QED strong-coupling regime that includes pure dipole dephasing and radiative decay both through the cavity mirror and into the side directions. This allows, for the first time, full modeling of the emission quantum efficiency, and the spectrum of the single photons emitted into the useful output mode of the, cavity.