Deterministic realization of collective measurements via photonic quantum walks

Understand

Collective measurements on identically prepared quantum systems can extract more information than local measurements, thereby enhancing information-processing efficiency.

• Although this nonclassical phenomenon has been known for two decades, it has remained a challenging task to demonstrate the advantage of collective measurements in experiments.
• Here we introduce a general recipe for performing deterministic collective measurements on two identically prepared qubits based on quantum walks.
• Using photonic quantum walks, we realize experimentally an optimized collective measurement with fidelity 0.9946 without post selection.