Direct generation of genuine single-longitudinal-mode narrowband photon pairs

Abstract

The practical prospect of quantum communication and information processing\nrelies on sophisticated single photon pairs which feature controllable\nwaveform, narrow spectrum, excellent purity, fiber compatibility and\nminiaturized design. For practical realizations, stable, miniaturized, low-cost\ndevices are required. Sources with one or some of above performances have been\ndemonstrated already, but it is quite challenging to have a source with all of\nthe described characteristics simultaneously. Here we report on an integrated\nsingle-longitudinal-mode non-degenerate narrowband photon pair source, which\nexhibits all requirements needed for quantum applications. The device is\ncomposed of a periodically poled Ti-indiffused lithium niobate waveguide with\nhigh reflective dielectric mirror coatings deposited on the waveguide\nend-faces. Photon pairs with wavelengths around 890 nm and 1320 nm are\ngenerated via type II phase-matched parametric down-conversion. Clustering in\nthis dispersive cavity restricts the whole conversion spectrum to one\nsingle-longitudinal-mode in a single cluster yielding a narrow bandwidth of\nonly 60 MHz. The high conversion efficiency in the waveguide, together with the\nspectral clustering in the doubly resonant waveguide, leads to a high\nbrightness of $3\\times10^4~$pairs/(s$\\cdot$mW$\\cdot$MHz). This source exhibits\nprominent single-longitudinal-mode purity and remarkable temporal shaping\ncapability. Especially, due to temporal broadening, we can observe that the\ncoherence time of the two-photon component of PDC state is actually longer than\nthe one of the single photon states. The miniaturized monolithic design makes\nthis source have various fiber communication applications.\n