Minimum resources for versatile continuous variable entanglement in integrated nonlinear waveguides

Abstract

In a recent paper [Phys. Rev. A {\bf 96}, 053822 (2017)], we proposed a strategy to generate bipartite and quadripartite continuous-variable entanglement of bright quantum states based on degenerate down-conversion in a pair of evanescently coupled nonlinear ${\chi }^{(2)}$ waveguides. Here, we show that the resources needed for obtaining these features can be optimized by exploiting the regime of second harmonic generation: the combination of depletion and coupling among pump beams indeed supplies all necessary wavelengths and appropriate phase mismatch along propagation. Our device thus entangles the two fundamental classical input fields without the participation of any harmonic ancilla. Depending on the propagation distance, the generated harmonics are entangled in bright or vacuum modes. We also evidence two-color bipartite and quadripartite entanglement over the interacting modes. The proposed device represents a boost in continuous-variable integrated quantum optics since it enables a broad range of quantum effects in a very simple scheme, which optimizes the resources and can be easily realized with current technology.

arXiv comment8 pages, 8 figures

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• Production of genuine multimode entanglement in circular waveguides with long-range interactions
• Coupling quasi-phase matching: entanglement buildup in ${\chi }^{(2)}$ nonlinear waveguide arrays
• Supermode-based second harmonic generation in a nonlinear interferometer
• Symmetry-based analytical solutions to the χ^{(2)} nonlinear directional coupler
• Unconditional remote entanglement using second-harmonic generation and twin two-mode squeezed vacuum states
• Continuous-variable spatio-spectral quantum networks in nonlinear photonic lattices