Quantum optics is a promising approach to demonstrate and apply many quantum phenomena. To use this approach for applications in e.g. quantum cryptography or quantum computing, the integration of several functional elements on one optical chip is of high importance. Using lithium niobate , a material with large transparency range as well as high nonlinear and electro-optic coefficients, we aim to implement sources for complex two-photon quantum states based on spontaneous parametric down-conversion. In arrays [4] and directional couplers [5] of coupled waveguides in lithium niobate we could already demonstrate generation and control of complicted spatially entangled quantum states.

Using integrated nanostructures for quantum optical applications allows to utilize the geometry-induced dispersion in such structures for control of the output quantum state. Additionally, it further minimizes the footprint of individual components, allowing for larger integration density.  Based on recently established nanofabrication technology for nanostructures in lithium niobate [6], we aim to design, manufacture and experimentally test sources for photon pairs, linear optical manipulation circuits and complex functional quantum devices on the lithium niobate platform.

[4] A. S. Solntsev, F. Setzpfandt, A. S. Clark, C. W. Wu, M. J. Collins, C. Xiong, A. Schreiber, F. Katzschmann, F. Eilenberger, R. Schiek, W. Sohler, A. Mitchell, C. Silberhorn, B. J. Eggleton, T. Pertsch, A. A. Sukhorukov, D. N. Neshev, and Y. S. Kivshar, "Generation of Nonclassical Biphoton States through Cascaded Quantum Walks on a Nonlinear Chip," Phys. Rev. X 4, 031007 (2014).

[5] F. Setzpfandt,  A. S. Solntsev, J. Titchener, C. W. Wu, C. Xiong, R. Schiek, T. Pertsch, D. N. Neshev, and A. A. Sukhorukov, "Tunable generation of entangled photons in a nonlinear directional coupler," Laser & Photonics Review 10, 131 (2016).

[6] R. Geiss, S. Diziain, M. Steinert, F. Schrempel, E.-B. Kley, A. Tünnermann, T. Pertsch, "Photonic crystals in lithium niobate by combining focussed ion beam writing and ion-beam enhanced etching," Phys. Status Solidi A-Appl. Mat. 211 (10), 2421-2425 (2014).

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