title: Large Cross-Phase Modulations at the Few-Photon Level.
abstract: We demonstrate an efficient cross-phase modulation (XPM) based on a closed-loop double-Λ system. The property of the double-Λ medium can be controlled by changing the phases of the applied optical fields. This phase-dependent XPM scheme can achieve large phase modulations at low-light intensities without requiring cavities or tightly focusing laser beams. With this scheme, we observe a π-level phase shift with two pulses, both consisting of eight photons in cold rubidium atoms. Such a novel scheme provides a simple route to generate strong interactions between photons and may have potential applications in all-optical quantum signal processing.
authors.affiliation: Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
authors.forename: Zi-Yu
authors.initials: ZY
authors.lastname: Liu
authors.affiliation: Department of Physics and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors.forename: Yi-Hsin
authors.initials: YH
authors.lastname: Chen
authors.affiliation: Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
authors.forename: Yen-Chun
authors.initials: YC
authors.lastname: Chen
authors.affiliation: Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
authors.forename: Hsiang-Yu
authors.initials: HY
authors.lastname: Lo
authors.affiliation: Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
authors.forename: Pin-Ju
authors.initials: PJ
authors.lastname: Tsai
authors.affiliation: Department of Physics and Frontier Research Center on Fundamental and Applied Sciences of Matters, National Tsing Hua University, Hsinchu 30013, Taiwan.
authors.forename: Ite A
authors.initials: IA
authors.lastname: Yu
authors.affiliation: Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan.
authors.forename: Ying-Cheng
authors.initials: YC
authors.lastname: Chen
authors.affiliation: Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan.
authors.forename: Yong-Fan
authors.initials: YF
authors.lastname: Chen