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Research Progress

Walk with Photon: Scientists Achieve Direct Measurement in Quantum Walk

Jun 28, 2018

Quantum walk has always been a useful model in quantum information, even universal quantum computation can be built up based on it. Although well understood in theory, its experimental implementation faces challenges in both scale and complexity.

In a study published online in Physical Review Letters, a research group led by Prof. LI Chuanfeng at University of Science and Technology of China of Chinese Academy of Sciences directly measured the winding number in a quantum walk for the first time by an up-to-50-step scale platform.

A novel way - the 'spin-orbit' coupling scheme by using the birefringent crystals cut collinearly - to improve the scale of the walk was promoted by Prof. LI’s group. This scheme avoided the intrinsic loss in traditional protocols and achieved ultra-stability.

Researchers demonstrated a 50-step Hadamard quantum walk of herald single photons within a high fidelity of 0.945.

Also, they developed a method to measure and reconstruct the final wave function, hence directly reading out the bulk topological invariants, i.e., winding numbers, in a quantum walk with chiral symmetry.

This photonic experimental setup scheme can benefit future study of other quantum walk phenomena and material topology.

The study was supported by Chinese Academy of Sciences, Ministry of Science and Technology, National Natural Science Foundation, Ministry of Education and China Postdoctoral Science Foundation.

 

Setup of the experiments (Image by XU Xiaoye)

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