Integrated optical single photon source "on demand" based on time multiplexing

• Applicant: Professorin Dr. Christine Silberhorn
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 235638099

The main objective is the development of an integrated optical, efficient true single photon source in the telecom regime, which is based on the probabilistic generation of a parametric downconversion (PDC) pair generation process. A time multiplexing scheme will be used to provide photons on demand with a high probability of triggered single photon generation and strongly suppressed multi-photon contributions. The source is based on integrated optical circuits realized in LiNbO3. Hereby a first circuit is used for photon pair generation via parametric down-conversion in a periodically poled waveguide section of the substrate. A subsequent monolithically integrated directional coupler then acts as a wavelength division multiplexer separating spatially the generated signal and idler photons. In order to enable time-multiplexing we will pump our device by a burst of pulses, where the signal photons can be used to herald the presence of single photons in the conjugate idler pulse. These idler photons are routed to a second integrated circuit with two electro-optic 2x2 switches and a fiber delay line. The second circuit serves as an active loop for overlapping different time slots to one single output time. Thereby, the first idler photon within the burst - which is heralded by detecting the corresponding signal photon - is routed by the first electro-optic switch to a fiber loop. At the end of the burst the stored photon is released via the second switch from that loop with adapted timing. For further improvement we will also test a photon number resolving detector for the heralding of single photons in the signal arm.The implementation of this source requires the development of specific integrated optical components and circuits. Key challenges are to minimize internal waveguide and interfacing losses between the different components - in particular at waveguide-fiber interfaces. Component design and the required fabrication processes will be devised and refined to meet these demands. Thereby the source will be developed step-by-step with a successively increasing complexity. We will perform detailed investigations to analyze the efficiency and brightness of the source, as well as the fidelity of the single photon generation. True single photons on demand, which will be produced by our source, should enable us to overcome one of the main drawbacks of state generation based on PDC. We will evaluate the performance of our device with respect to applications in quantum information processing. This will provide us with realistic benchmarks on the practical usability of such sophisticated integrated optics devices for future quantum technology.

• DFG Programme: Research Grants