Barkhofen, Sonja and Lorz, Lennart and Nitsche, Thomas and Silberhorn, Christine and Schomerus, Henning Ulrich (2018) Supersymmetric Polarization Anomaly in Photonic Discrete-Time Quantum Walks. Physical review letters, 121 (26). ISSN 1079-7114
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Abstract
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.