Generation and active manipulation of qubits in LiNbO3-based integrated circuits

We present and discuss perspectives on developing advanced quantum optical circuits monolithically integrated in the lithium niobate platform. A set of basic components comprising photon pair sources based on parametric down conversion (PDC), passive routing elements and active electrooptically controllable switches and polarisation converters are constituent parts of a toolbox which is the basis for a broad range of diverse quantum circuits. We discuss the state of the art of these components and present models that properly describe their performance in quantum circuits. As a demonstration of the applicability of these models we consider as an example an on-chip two-photon interference circuit comprising a PDC section for photon pair generation followed by an actively controllable modified Mach-Zehnder structure for detecting Hong-Ou-Mandel (HOM) interference. The performance of such a chip is simulated theoretically by taking even imperfections in the properties of the individual components into account.