University of Science and Technology of China has developed an optical quantum simulator to study the mechanism of phase transition

<p> The research team of Professor Li Chuanfeng of the Key Laboratory of Quantum Information of the Chinese Academy of Sciences led by Academician Guo Guangcan of the University of Science and Technology of China successfully developed an optical quantum simulator, and for the first time confirmed the adiabatic of the Kibble-Zurek (KZ) theory describing the phase transition process in a pure quantum model— The pulse is approximately true. This result was published in the Physical Review Letters.

Quantum computers have huge advantages that classic computers cannot match. Restricted by technology, people cannot yet realize universal universal quantum computers. However, with the rapid development of quantum information technology, people can already use some quantum systems to achieve some special quantum computing functions. This type of quantum computer for special tasks is a quantum simulator. The quantum simulator developed by the research group is for the special problem of KZ mechanism in quantum phase transition.

The standard model of continuous phase transitions believes that symmetrical breakage will accompany the second-order phase transition. However, little is known about the phase transition dynamics near the shortcomings of symmetrical breakage. Professor Kibble, a famous expert in high-energy physics and cosmology, found that the topological defects of the phase transition are related to the characteristics of the phase change dynamics when studying the phase transition problem of the early universe. Therefore, the phase transition dynamics can be studied by observing the topological defects. Subsequently, Professor Zurek, the founder of quantum decoherence theory, further research found that this mechanism in cosmology also holds true in the continuous phase transition of the condensed state. This theory is called the Kibble-Zurek theory. The core of this theory is adiabatic-pulse approximation. Under this approximation, the kinetic process of continuous phase transition can be divided into adiabatic-pulse-adiabatic three processes, so that the phase can be obtained The relationship between the density of variable topological defects and the speed of sudden changes in dynamics. In the classic phase transition, the KZ theory has been confirmed by many experiments, but the KZ mechanism in the quantum system has not been verified by any experiment.

The optical quantum simulator developed by Li Chuanfeng's research group is composed of nine-level interference devices. This is the highest-level optical device in the world by far. It is the first real optical quantum simulator. The existing optical quantum simulation experiments need to know the quantum state of the simulated system in advance, so it is essentially the quantum state preparation process. The research team used this optical quantum simulator to prove for the first time that the adiabatic-pulse hypothesis is true in the pure quantum model with extremely high accuracy (total visibility of nine-level interference device reaches 97.5%). This achievement lays a solid foundation for further verifying the effectiveness of KZ theory in quantum phase transitions and for further development of quantum simulators to solve more complex problems.

Reviewers believe that the quantum simulator "has extremely high interference visibility", and the experimental results given "are consistent with the theoretical results with surprising accuracy". Starting point ". Moreover, "their work will promote the interest of non-equilibrium quantum phase transition dynamics in the field of quantum optics." Zurek et al. In the review article (arXiv: 1310.1600) written by Kure on the 80th birthday of Kibble Introduce this achievement in one section.

The above research was supported by the Ministry of Science and Technology, the Fund Committee and the Chinese Academy of Sciences.

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