USTC successfully applied superconducting quantum processor to the study of quantum many-body system
Quantum technology and quantum many-body systems have been extensively studied by physicists in recent years. Two imbalanced dynamic processes of particular interest in this field are quantum thermalization and information perturbation. "Thermalization" is the process by which a quantum many-body system achieves thermal equilibrium; on the other hand, "information disturbance" requires dispersing local information in the many-body quantum entanglement of the entire quantum many-body system.
The team of Pan Jianwei and Zhu Xiaobo of the University of Science and Technology of China recently observed thermalization and information disturbance in a superconducting quantum processor. Their research results, published in Physical Review Letters under the title "Observation of Thermalization and Information Perturbation in Superconducting Quantum Processors" [1], are expected to pave the way for new research on the thermodynamics of quantum many-body systems.
"The non-equilibrium properties of quantum many-body systems are related to whether the non-integrability of quantum systems is broken," Zhu Xiaobo said. "Specifically, in the non-equilibrium dynamic process of one-dimensional free fermions as an integrable system, thermal Changes and disruption of information will fail.”
Two key reasons why the experimental study of thermalization and information perturbation in both integrable and nonintegrable quantum systems is particularly challenging are: First, doing so requires experimental implementation of both types of systems on the same quantum simulator . Furthermore, to successfully conduct these experiments, researchers need to be able to collect accurate and valid measures of entanglement entropy and tripartite mutual information. These measurements ultimately allow scientists to quantify thermalization and perturbation of information, a process typically using a method called "multi-qubit quantum state tomography."
"In our recent work, using a ladder-structured programmable superconducting circuit consisting of 24 qubits, we experimentally investigated thermalization and scrambling in 12-qubit chains and ladders, quantifying the one-dimensional XX model. simulation, the model can be mapped to free fermions which is a typical integrable system, while the ladder XX model is a non-integrable system," Zhu Xiaobo explained [2], "Finally, we observed that the qubit array chain and the ladder diagram two distinct dynamical behaviors, demonstrating that integrability plays a key role in thermalization and information scrambling."
Superconducting quantum circuits and experimental pulse sequences. (a) Optical micrograph of the superconducting circuit. Each qubit has an independent XY and Z control line (yellow area) coupled to an independent readout resonator (purple area). (b) Schematic diagram of the superconducting quantum circuit. The arrows above and below indicate the initial states of the qubits as |1⟩ and |0⟩, respectively. Qubits Q1-Q12 are used in the quantum simulation of the XX chain. Qubits Q1-Q6 and Q13-Q18 are used in the quantum simulation of the XX ladder. (c), (d) are the experimental pulse sequences for the quantum simulation of XX chains and ladders, respectively. The pulse sequence includes initialization, evolution and readout. During initialization, all qubits are in the |0⟩ state, and the X gate is used to select the qubits whose initial state is |1⟩. Next, the qubits are tuned to the operating point by Z pulses, and time evolution is achieved. Finally, the measurements are taken after the qubit is turned back to its idle point.
Zhu Xiaobo et al. study quantum thermalization and information perturbation in a superconducting quantum processor characterized by high programmability: by tuning all qubits to the same interaction frequency, they were able to experimentally study qubit chains and trapezoids Non-equilibrium dynamics of Fig. Zhu Xiaobo said: "After time evolution, we can measure local observation variables by projecting all qubits onto the Z projection. We also use high-precision multi-qubit quantum state tomography to measure entanglement entropy and tripartite mutual information ( TMI). The ladder structure of superconducting circuits allows us to study integrable one-dimensional chains and non-integrable ladders in the same quantum processor."
The research team first analyzed thermalization and information perturbation in qubit array chains and ladder diagrams of their highly programmable superconducting circuits. The observations show that integrability significantly affects the properties of nonequilibrium quantum many-body systems.
Dynamic variation of local density and operator distance. (a) Experimental data on the time evolution of local observations n|1⟩(t) in quantum chain and ladder graphs. (b) is similar to (a), but corresponds to the local observation n|0⟩(t). (c) Time evolution of operator distances between quenched and thermal states in chains and ladders. The solid line is a value that does not consider decoherence.
Zhu Xiaobo said: "We also observed a stable negative value of TMI in a non-rectified system, which is the first experimental feature of information scrambling characterized by TMI, which lays the foundation for further experimental research on TMI on other platforms."
Information scrambled by TMI quantization. (a) Illustrated experimental pulse sequence for the dynamic study of the TMI of qubit chains. (b) Similar to (a), but for qubit ladder diagrams. (c) Numerical results of the TMI time evolution of quantum chains and ladder graphs without considering decoherence, with mean values of −0.283 and −0.42, respectively (highlighted by dashed lines). (d) Experimental data on the time evolution of TMI for qubit chains and ladder graphs, with mean values of −0.106 and −0.196, respectively (dashed lines are highlighted).
In addition to gathering insights into how the integrability of a system determines its non-equilibrium properties and revealing the characteristics of information scrambling, Zhu Xiaobo et al. are also the first teams to study quantum many-body systems using highly programmable quantum processors.
In the future, the size of the circuits they used could be further expanded to perform calculations that are more difficult for classical computers to perform. In future studies, the researchers hope to expand on their recent work to pursue two other main research directions: "First, we plan to run more qubits to form a larger many-body system," Zhu Xiaobo added, "Secondly, we plan to improve the programmability of quantum processors. With the state-of-the-art superconducting quantum processor, Zu Chongzhi 2.0, we have successfully demonstrated the superiority of quantum computing. We plan to use this processor to demonstrate many-body physics more exciting phenomena in the future.”
Reference link:
[1] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.160502
[2]https://phys.org/news/2022-05-thermalization-scrambling-superconducting-quantum-processor.html
