Mainz 2017 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 26: Quantum Optics IV

Q 26.2: Talk

Tuesday, March 7, 2017, 14:45–15:00, P 5

Spectrally filtered photon pairs cannot be both pure and efficient — •Evan Meyer-Scott, Nicola Montaut, Linda Sansoni, Harald Herrmann, Tim J. Bartley, and Christine Silberhorn — Universität Paderborn, Integrierte Quantenoptik, Warburger Str. 100, D-33098 Paderborn

Photon pairs from spontaneous parametric down conversion or four-wave mixing are widely employed in quantum cryptography, quantum computing, and fundamental physical tests. For photons from separate sources to interfere, for example for entanglement swapping, linear optical quantum computing, or quantum walks, the photons must be spectrally pure. This requires that the frequency of each photon in the pair be uncorrelated with the other’s, which can be achieved by narrowband filtering each photon. Here we show that this filtering comes at a direct cost of heralding efficiency, the efficiency to detect one photon of the pair given a detection of the other. We find this effect is fundamental rather than technical, and independent of filter shape and filter, pump, and phasematching bandwidth, but can be eliminated by source engineering to bring the phasematching angle to a certain range. We support our analytical and numerical results with an experiment that directly shows the tradeoff between purity and heralding efficiency.