title: Cross modulation of two laser beams at the individual-photon level.
abstract: Deterministic photon-photon interactions are a long-standing goal in optical science. Using an atomic ensemble inside a cavity, we demonstrate the mutual cross modulation of two continuous light beams at the level of individual photons. The originally uncorrelated beams derived from independent lasers become anticorrelated, as evidenced by an equal-time cross-correlation function g^{(2)}=0.89(1), showing that one photon in one beam extinguishes a photon in the other beam with a probability of 11(1)%. With further technical improvements, our approach should enable the nondestructive continuous detection of traveling optical photons.
authors.affiliation: Department of Physics and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Kristin M
authors.initials: KM
authors.lastname: Beck
authors.affiliation: Department of Physics and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Wenlan
authors.initials: W
authors.lastname: Chen
authors.affiliation: Department of Physics and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Lin
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA and Joint Quantum Institute, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Gullans
authors.affiliation: Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Mikhail D
authors.initials: MD
authors.lastname: Lukin
authors.affiliation: Department of Physics and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
authors.forename: Vladan
authors.initials: V
authors.lastname: Vuletić