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Science | important progress has been made in quantum simulation of ultracold atoms

Pan Jianwei and Yuan Zhensheng of the University of science and technology of China have made progress in the quantum simulation of ultra cold atoms in cooperation with researchers from the University of Heidelberg in Germany, the University of Innsbruck in Austria and the University of Trento in Italy. Using the quantum simulator of ultracold atoms, researchers simulated the heating dynamics of the transition from non-equilibrium state to equilibrium state in the lattice gauge field theory. For the first time, they experimentally confirmed the”loss” of initial state information caused by quantum multi-body heating under the constraint of gauge symmetry, and made important progress in solving complex physical problems by using quantum simulation methods. Relevant research results were published in science.

Gauge field theory is the basis of modern physics, such as quantum electrodynamics and standard models that describe the interaction of basic particles. It is a gauge field theory that meets the symmetry of specific groups, and has been widely used in particle physics, cosmology, condensed matter physics and other fields. Because of its high complexity, there are still many open problems in the gauge field theory system. Among them, whether the physical system described by gauge field theory can evolve from far from equilibrium to thermal equilibrium has attracted much attention. The solution of this problem is helpful to understand the problem of heavy nuclear collision in high-energy physics, and will also provide a physical explanation for the formation of matter in the early stage of the big bang in modern cosmology. However, using classical computers to solve the complex gauge field theory is a recognized problem, and quantum simulators provide a new way to solve this problem.

In recent years, scientists have tried to carry out quantum simulation research on lattice gauge field theory with ion trap, ultra cold atomic gas, Rydberg atomic array and superconducting qubit systems. However, due to the complex form of interaction in the lattice gauge theory and the requirement that the physical system is always constrained by the local gauge symmetry, it is difficult to simulate the experimental thermodynamics of the lattice gauge field theory, so it has not been realized experimentally.

In order to solve the two main problems of too few coherent particles and unable to guarantee the constraint of gauge symmetry in the quantum simulator, the scientific researchers of the University of science and technology of China have developed unique quantum control and measurement technologies such as spin dependent superlattice, microscope absorption imaging, particle number resolution detection, etc. in the ultra cold atom quantum simulator, the deep cooling of atoms in the optical lattice is proposed and realized, and the high temperature of the quantum simulator is solved For the problem of too many defects, we have experimentally prepared a large-scale quantum simulator at the level of nearly 100 atoms [science 369, 550 (2020)]; The experimental simulation of the quantum phase transition process of lattice gauge field theory using a large-scale quantum simulator is realized for the first time, and the gauge invariance in the process is verified [Nature 587, 392 (2020)]. On the basis of the above research, through the combination of experiment and theory, the team prepared the system to an initial state far from equilibrium. For the first time, the team experimentally studied the influence of gauge symmetry constraints on the heating dynamics of quantum multibody systems, observed the process of heating different initial states with the same conservation to the same equilibrium state, and verified the”loss” of initial state information of quantum multibody systems caused by the heating process, The relationship between the early nonequilibrium dynamics and the final thermal equilibrium state of gauge field theory is established, and important progress has been made in solving complex physical problems using large-scale quantum simulators.

In the future, the team will further use quantum simulation methods to study gauge field theoretical models with other group symmetries and higher spatial dimensions, as well as physical problems such as vacuum decay and dynamic topological quantum phase transition. The reviewers of science magazine spoke highly of this and believed that this research had made an important contribution to the development of the field of ultra cold atom simulation lattice gauge field theory and represented the frontier of quantum simulation research. The research work was supported by the Ministry of science and technology, the National Natural Science Foundation of China, the Chinese Academy of Sciences, the Ministry of education and Anhui Province.

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