title: Large conditional single-photon cross-phase modulation.
abstract: Deterministic optical quantum logic requires a nonlinear quantum process that alters the phase of a quantum optical state by π through interaction with only one photon. Here, we demonstrate a large conditional cross-phase modulation between a signal field, stored inside an atomic quantum memory, and a control photon that traverses a high-finesse optical cavity containing the atomic memory. This approach avoids fundamental limitations associated with multimode effects for traveling optical photons. We measure a conditional cross-phase shift of [Formula: see text] (and up to [Formula: see text] by postselection on photons that remain in the system longer than average) between the retrieved signal and control photons, and confirm deterministic entanglement between the signal and control modes by extracting a positive concurrence. By upgrading to a state-of-the-art cavity, our system can reach a coherent phase shift of π at low loss, enabling deterministic and universal photonic quantum logic.
authors: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139; Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors: Kristin M
authors: 0000-0003-2486-4164
authors: KM
authors: Beck
authors: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139; Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors: Mahdi
authors: M
authors: Hosseini
authors: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139; Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139.
authors: Yiheng
authors: Y
authors: Duan
authors: Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139; Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139 vuletic@mit.edu.
authors: Vladan
authors: V
authors: Vuletić
keywords: cavity quantum electrodynamics; cross-phase modulation; electromagnetically induced transparency; photonic quantum gate; single-photon Kerr nonlinearity