Supersymmetric Polarization Anomaly in Photonic Discrete-Time Quantum Walks.

Area of Science:

• Quantum physics
• Topological effects
• Optical networks

Background:

• Quantum anomalies cause finite expectation values, challenging system symmetries.
• These anomalies are crucial for topological effects in various systems but are difficult to observe directly.
• Previous experimental methods for observing these anomalies were complex and infeasible.

Purpose of the Study:

• To implement an optical-network realization of a discrete-time quantum walk.
• To directly observe quantum anomalies via the circular polarization of topological midgap states.
• To overcome experimental limitations of previous multi-step protocols with a single-step approach.

Main Methods:

• Utilized a single-step discrete-time quantum walk protocol in an optical network.
• Combined chiral symmetry with a unitary version of supersymmetry in the system's evolution.
• Performed full polarization tomography by accessing the walker's position and coin state.

Main Results:

• Direct observation of a quantum anomaly in the circular polarization of a topological midgap state.
• Evidence supporting the predicted anomaly of midgap states was provided through polarization tomography.
• Demonstrated a feasible single-step protocol for observing quantum anomalies.

Conclusions:

• The study successfully demonstrated a direct observation of quantum anomalies in an optical network.
• This work paves the way for dynamically distilling topological states for quantum information applications.
• The developed single-step protocol offers a more experimentally accessible method for studying topological phenomena.