Deterministic realization of collective measurements via photonic quantum walks

TL;DR

This paper demonstrates a deterministic method for collective measurements on two qubits using photonic quantum walks, achieving high fidelity and improved quantum state tomography efficiency.

Contribution

It introduces a general recipe for deterministic collective measurements on qubits via photonic quantum walks, with experimental realization and high fidelity.

Findings

Achieved a measurement fidelity of 0.9946 without post selection.

Realized the highest efficiency in qubit state tomography to date.

Provided a practical approach to surpass local measurement limits in quantum information processing.

Abstract

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. As an application, we achieve the highest tomographic efficiency in qubit state tomography to date. Our work offers an effective recipe for beating the precision limit of local measurements in quantum state tomography and metrology. In addition, our study opens an avenue for harvesting the power of collective measurements in quantum information processing and for exploring the intriguing physics behind this power.