We demonstrate the efficient generation of narrow-bandwidth photons and photon superposition states. Since the heralded states stem from a transient collective spin excitation in the atomic ensemble, this work allows engineering of arbitrary collective atomic excitation states.
We demonstrate efficient heralded generation of high purity narrow-bandwidth single photons from a transient collective spin excitation in a hot atomic vapor cell. Employing optical homodyne tomography, we fully reconstruct the density matrix of the generated photon and observe a Wigner function reaching the zero value without correcting for any inefficiencies. The narrow bandwidth of the photon produced is accompanied by a high generation rate yielding a high spectral brightness. The source is, therefore, compatible with atomic-based quantum memories as well as other applications in light-atom interfacing. This Letter paves the way to preparing and measuring arbitrary superposition states of collective atomic excitations.
This thesis presents a study of the four-wave mixing process in hot Rubidium vapor and its applicability to generating arbitrary quantum states, both in the optical domain and as atomic collective spin excitations. The four-wave mixing process involves a double Raman scattering event, where conservation of energy and momentum entangle these Raman-scattered photons. Heralding upon detection of one of these photons in a given mode projects the other photon onto a single photon Fock state in a well-defined mode, which may serve as a narrowband quantum light source that is compatible with atom-based quantum communication protocols. We integrate the existing technique of conditional measurements into our detection scheme, which allows us to engineer more complex quantum states. Experimentally we demonstrate the production of arbitrary superpositions of |0> and |1> in the optical Fock basis. We also present a theoretical model of this process which incorporates experimental complications such as losses, higher photon-number states, and a non-trivial temporal mode. This scheme can be extended to generate arbitrary quantum states with increasing photon numbers, at the expense of repetition rate. The atomic nature of this four-wave mixing process has an added benefit in that it allows access to excitations of the collective atomic ensemble. The optical results demonstrate the creation of transient collective spin excitations, and we present a proposal to extend this work to generate longer lived arbitrary collective atomic states.