PAN's Superconducting Quantum Experiment Team applied superconducting qubits in quantum walks and published the work in Science on May 2. It is expected to have a great influence on the research of simulation of many-body physical phenomena and universal quantum computation with quantum walks in the future. 

While simulating complex quantum many-body systems, the computation complexity of classical computation grows exponentially with particle number — in other words, increases several times whenever one more particle is involved. Hence, it's urgent to promote the development of the quantum computation, which can fuel exploration in areas from macroscopic to microscopic, including the human genetic map and the celestial body evolution. Developing this technology, however, first requires sufficient entangled qubits and deducting the correlation between them. 

Superconducting quantum computing is based on solid state systems and inherently holds an advantage in scalability, making it one of the most promising proposals for quantum computation. Currently, the biggest challenge is to ensure the quality of all qubits while continually integrating more qubits. 

Quantum walks are essential to simulating large-scale many-body systems and realizing universal quantum computation in theory. Random walks refer to the irregular movements of objectsin a region. Classical random walks are used to describe physical phenomena like Brownian motion and diffusion in the classical physical mechanics, and quantum walks are the analogs of classical random walks in the quantum mechanics. Due to the quantum superposition, the behaviors of particles moving on the lattice need to be described by the statistical law of wave function of quantum mechanics. 

Before this work, PAN Jianwei and his colleagues ZHU Xiaobo, LU Chaoyang, PENG Chengzhi have successfully generated 12-qubit genuine entanglement in cluster states, which broke the world record of superconducting qubit entanglement. Especially, their proposal is easier to scale to more qubits than previous. 

This time, the research team experimentally demonstrate the quantum walks of the strongly correlated entanglement system for the first time worldwide, based on the precedent high-quality solid-state quantum computation system with sufficient quantum entangled qubits. They investigated the behaviors of quantum walks under single-particle and two-particle excitation, observed the propagation and evolution of quantum entanglement during quantum walks, as well as the Fermization of two-photon in the strongly correlated photon system. This work lays the foundation for further studies on many-body physical phenomena and universal quantum computation using quantum random walks. 

The research team is led by Prof. PAN Jianwei, ZHU Xiaobo and PENG Chengzhi from University of Science and Technology of China (USTC), in alliance with the theoretical research group led by FAN Wei from the Institute of Physics of the Chinese Academy of Sciences.