Quantum anomalies lead to finite expectation values that defy the apparent symmetries of a system. These anomalies are at the heart of topological effects in electronic, photonic, and atomic systems, where they result in a unique response to external fields but generally escape a more direct observation. Here, we implement an optical-network realization of a discrete-time quantum walk, where such an anomaly can be observed directly in the unique circular polarization of a topological midgap state. We base the system on a single-step protocol overcoming the experimental infeasibility of earlier multistep protocols. The evolution combines a chiral symmetry with a previously unexplored unitary version of supersymmetry. Having experimental access to the position and the coin state of the walker, we perform a full polarization tomography and provide evidence for the predicted anomaly of the midgap states. This approach opens the prospect to dynamically distill topological states for quantum information applications.
CITATION STYLE
Barkhofen, S., Lorz, L., Nitsche, T., Silberhorn, C., & Schomerus, H. (2018). Supersymmetric Polarization Anomaly in Photonic Discrete-Time Quantum Walks. Physical Review Letters, 121(26). https://doi.org/10.1103/PhysRevLett.121.260501
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