Collective measurements on identically prepared quantum systems can extractmore information than local measurements, thereby enhancinginformation-processing efficiency. Although this nonclassical phenomenon hasbeen known for two decades, it has remained a challenging task to demonstratethe advantage of collective measurements in experiments. Here we introduce ageneral recipe for performing deterministic collective measurements on twoidentically prepared qubits based on quantum walks. Using photonic quantumwalks, we realize experimentally an optimized collective measurement withfidelity 0.9946 without post selection. As an application, we achieve thehighest tomographic efficiency in qubit state tomography to date. Our workoffers an effective recipe for beating the precision limit of localmeasurements in quantum state tomography and metrology. In addition, our studyopens an avenue for harvesting the power of collective measurements in quantuminformation processing and for exploring the intriguing physics behind thispower.
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