Nonlinear Optical Interfaces for Quantum Information and Networking

Associate Professor Kejie Fang

Abstract: Optical nonlinearities provide essential capabilities for quantum information processing and networking, yet many applications remain limited by weak nonlinear interactions and optical loss. In this talk, I will present an integrated photonics platform based on the III–V semiconductor indium gallium phosphide (InGaP) that addresses these limitations by combining strong second-order nonlinearity with low loss. This combination enables a high nonlinearity-to-loss ratio and nonlinear conversion efficiencies one to two orders of magnitude above prior benchmarks. I will highlight applications including broadband entangled photon generation, efficient quantum frequency conversion between telecom and visible wavelengths, and magnet-free optical nonreciprocity on chip. I will then move from pump-enhanced nonlinear processes to interactions between individual photons. First, I will describe a nonlinear Bell-state analyzer based on sum-frequency generation in an InGaP microcavity, enabling high-fidelity quantum teleportation while suppressing multiphoton errors associated with probabilistic entangled photon sources. Finally, I will show how passive broadband nonlinearity and interference generate nonclassical correlations between photons. Together, these results demonstrate how improving the balance between nonlinear interaction and loss enables high-performance photonic interfaces, advancing quantum information processing and quantum networking.

Bio: Kejie Fang received his B.S. in physics from Peking University and his Ph.D. in physics from Stanford University, where he worked with Prof. Shanhui Fan. He was then a postdoctoral scholar and senior research scientist at Caltech in the Department of Applied Physics and Materials Science, working with Prof. Oskar Painter. He is an Associate Professor and Yuen T. Lo Faculty Fellow in the Department of Electrical and Computer Engineering at the University of Illinois Urbana-Champaign, and is affiliated with the Department of Physics. His group develops integrated nonlinear and quantum photonic devices for quantum information processing, networking, and sensing, and pioneered the InGaP integrated quantum photonics platform. His research is supported by DARPA, ONR, NSF, and DOE, and he is a co-investigator in the NSF HQAN Quantum Leap Challenge Institute and the DOE Q-NEXT National Quantum Information Science Research Center. He is a recipient of the NSF CAREER Award.