A cold atom cloud is an interesting medium which allows both generation of entangled photons with unique properties and coherent storage of photons. In this talk, I will first describe our work on complete characterization of the narrowband entangled photons from cold atoms. Our stimulated emission tomography technique has allowed measurement of both joint temporal intensity (JTI) and joint temporal phase (JTP) of the entangled photons, hence providing the complete frequency-time two-photon wavefunction of the narrowband entangled photons from cold atoms. We show over six orders of magnitude improvement in the measurement time for obtaining JTI and JTP compared to the conventional direct photon counting method, thus paving the way toward ultrafast high-resolution quantum tomography of photonic quantum states. I will then report on our latest work on demonstration of the single-photon stationary light pulse (SLP) in a cold atomic ensemble. A single collective atomic excitation is created and heralded by detecting a Stokes photon in the spontaneous Raman scattering process. The heralded single atomic excitation is converted into a single stationary optical excitation or the single-photon SLP, whose eﬀective group velocity is zero, eﬀectively forming a trapped single-photon pulse within the cold atomic ensemble. The single-photon SLP is then released from the atomic ensemble as an anti-Stokes photon after a speciﬁed trapping time. The second-order correlation measurement between the Stokes and anti-Stokes photons reveals the nonclassical nature of the single-photon SLP. Our work paves the way toward quantum nonlinear optics without a cavity.
Prof. Yoon-Ho Kim received Ph.D. in quantum optics from the University of Maryland, Baltimore County (USA) in 2001. He then held the prestigious Eugene P. Wigner Fellowship at the Oak Ridge National Laboratory (USA). Since 2004, he has been on the faculty of the Pohang University of Science and Technology (POSTECH) in Korea. His recent interests include weak quantum measurement in quantum information, multi-photon quantum systems, quantum/ghost imaging, and atom-photon interactions. He is currently serving as an Associate Editor for Optics Express and as an editor for the Journal of the Korean Physical Society.