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Experimental system. (a) Schematic of the ultracold atom microscope and the prepared |Z2⟩ Initial state. We combine the optical superlattices and the addressing beam generated by the digital micromirror device (DMD) to prepare the initial |Z2⟩ state The top shows an example fluorescence image of raw data of the atomic distribution of the initial |Z2⟩ state in a single experimental realization. (b) The physical model with bosons in a one-dimensional optical lattice with alternating deep and shallow lattice sites. Here, U denotes the on-site interaction strength, J denotes the boson hopping amplitude, δ denotes the energy shift between neighboring shallow and deep lattices, and Δ denotes the per-site linear tilt. Open, filled circles with + or − denote zero physical charge, +1 or −1 at matter sites, and arrows denote electric field. (c) An Ising-type quantum phase transition by m/˜t tuning. Credit: Physical Examination Letters (2023). DOI: 10.1103/PhysRevLett.131.050401
Researchers from the University of Science and Technology of China (USTC), Chinese Academy of Sciences (CAS) have developed an ultracold atom quantum simulator to study the relationship between the non-equilibrium thermalization process and criticality quantum in lattice gauge field theories. . The research was led by Pan Jianwei and Yuan Zhensheng, in collaboration with Zhai Hui of Tsinghua University and Yao Zhiyuan of Lanzhou University.
Their results reveal that multi-body systems possessing gauge symmetry tend to thermalize more easily toward an equilibrium state when they are located in an equilibrium state. quantum phase transition critical region. The results were published in Physical Examination Letters.
Gauge theory And statistical mechanics are two fundamental theories of physics. From Maxwell’s equations of classical electromagnetism to quantum electrodynamics and the Standard Model, which describe the interactions of fundamental particles, all adhere to specific gauge symmetries. On the other hand, statistical mechanics relates the microscopic states of large sets of particles (such as atoms and molecules) to their macroscopic statistical behaviors, based on the principle of maximum entropy proposed by Boltzmann and others. It explains, for example, how the energy distribution of microscopic particles affects macroscopic quantities such as pressure, volume or temperature.
So, does an many-body quantum system described by gauge theory thermalize to a thermodynamic equilibrium when it is far from equilibrium? Answering this question would advance our understanding of gauge theory, statistical mechanics and their interrelationships. While theoretical physicists having proposed various models To analyze this problem, it remains experimentally difficult to construct a physical system which is both described by gauge theory and which can be artificially manipulated and observed during its thermalization process.
The emergence of ultracold atomic quantum simulators has provided an ideal experimental platform to study gauge theories and statistical physics simultaneously. In 2020, a USTC research team developed an ultra-cold atomic optical lattice quantum simulator with 71 lattice points. This was the first experimental simulation of the quantum phase transition process in U(1) lattice gauge theory, particularly in the Schwinger model.
In 2022, the team simulated the thermalization dynamics of the transition from a non-equilibrium state to an equilibrium state in lattice gauge field theories. For the first time experimentally, they verified the “loss” of initial state information due to many-body quantum thermalization under gauge symmetry constraints.
The collaborators of this project, Zhai Hui and Yao Zhiyuan, highlighted this through theoretical research that there is a correlation between quantum thermalization and quantum phase transitions in such lattice gauge models. Starting from the antiferromagnetic Neel state, they predicted that the system could only achieve full thermalization near the quantum phase transition point.
Observing the relationship between quantum thermalization and quantum phase transitions in lattice gauge theories poses new challenges to previous experimental capabilities: the challenge lies in how to control and detect many-body quantum states in situ with single lattice point precision and distinctive atomic numbers.
Based on their ultracold atomic quantum simulator, the team combined techniques such as quantum gas microscopy, spin-dependent superlattices, and programmable optical potentials. This fusion paved the way for the development of atomic operations and detection techniques with single-site precision and distinctive particle numbers.
Taking advantage of these advances, researchers have been able to prepare and probe multi-atomic quantum states with any atomic configuration. Furthermore, they followed the dynamic evolution of many-body quantum states under the constraints of gauge symmetry.
In their study, the team experimentally prepared initial states with specific atomic configurations. They used the method of adiabatic evolution to study the quantum phase transition process under gauge symmetry constraints. For the first time under experimental conditions, they accurately identified the phase transition point using finite size scale theory.
Additionally, they explored the dynamics of annealing the same initial configuration away from equilibrium. Their work revealed a model that many-body systems with gauge symmetry, when near the critical point of quantum phase transition, tend to stabilize thermally at a equilibrium state.
The newspaper Physics highlighted their achievements in an article titled “Watching a quantum system thermalize“.
More information:
Han-Yi Wang et al, Interdependent thermalization and quantum criticality in a lattice gauge simulator, Physical Examination Letters (2023). DOI: 10.1103/PhysRevLett.131.050401
Charles Day, Watching a quantum system thermalize, Physics (2023). DOI: 10.1103/Physique.16.s115
Journal information:
Physical Examination Letters
Provided by University of Science and Technology of China
