Direct characterization of a nonlinear photonic circuit's wave function with laser light
Abstract
Integrated photonics is a leading platform for quantum technologies including nonclassical state generation Vergyris:2016-35975:SRP, Solntsev:2014-31007:PRX, Silverstone:2014-104:NPHOT, Solntsev:2016:RPH, demonstration of quantum computational complexity LamitralNJP2016 and secure quantum communications Zhang:2014-130501:PRL. As photonic circuits grow in complexity, full quantum tomography becomes impractical, and therefore an efficient method for their characterization Lobino:2008-563:SCI, Rahimi-Keshari:2011-13006:NJP is essential. Here we propose and demonstrate a fast, reliable method for reconstructing the two-photon state produced by an arbitrary quadratically nonlinear optical circuit. By establishing a rigorous correspondence between the generated quantum state and classical sum-frequency generation measurements from laser light, we overcome the limitations of previous approaches for lossy multimode devices Liscidini:2013-193602:PRL, Helt:2015-1460:OL. We applied this protocol to a multi-channel nonlinear waveguide network, and measured a 99.280.31\% fidelity between classical and quantum characterization. This technique enables fast and precise evaluation of nonlinear quantum photonic networks, a crucial step towards complex, large-scale, device production.
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