title: Ramsey Interference with Single Photons.
abstract: Interferometry using discrete energy levels of nuclear, atomic, or molecular systems is the foundation for a wide range of physical phenomena and enables powerful techniques such as nuclear magnetic resonance, electron spin resonance, Ramsey-based spectroscopy, and laser or maser technology. It also plays a unique role in quantum information processing as qubits may be implemented as energy superposition states of simple quantum systems. Here, we demonstrate quantum interference involving energy states of single quanta of light. In full analogy to the energy levels of atoms or nuclear spins, we implement a Ramsey interferometer with single photons. We experimentally generate energy superposition states of a single photon and manipulate them with unitary transformations to realize arbitrary projective measurements. Our approach opens the path for frequency-encoded photonic qubits in quantum information processing and quantum communication.
authors.affiliation: School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Clemmen
authors.affiliation: School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Farsi
authors.affiliation: Faculty of Physics, Humboldt-University Berlin, Berlin 12489, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Ramelow
authors.affiliation: School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA.|Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA.
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Gaeta