From periodically driven quantum materials to engineered quantum simulators, time-dependent driving has become a powerful tool for creating novel non-equilibrium phases that do not exist in static systems. Examples include discrete time crystals and Floquet topological phases. However, breaking continuous time-translation symmetry typically leads to a generic outcome: driven quantum systems absorb energy and eventually heat up toward a featureless infinite-temperature state, where coherent structure is lost.

Understanding how fast this heating occurs—and whether it can be controlled—has become a central challenge in non-equilibrium physics. While high-frequency periodic driving is known to delay heating, much less is understood about heating dynamics under more general, non-periodic driving protocols.

In a recent study, researchers implemented a random multipolar driving scheme on a large superconducting quantum processor and directly observed a long-lived prethermal regime, where the system temporarily avoids full thermalization. The experiment was carried out on Chuang-tzu 2.0, a two-dimensional superconducting processor consisting of 78 qubits arranged in a 6×13 lattice with 137 tunable couplers.

The system was initialized in a density-wave configuration and then driven by a sequence of randomly structured control pulses characterized by two parameters: the driving order and the duration of each driving unit. By monitoring particle-number imbalance and entanglement entropy growth during time evolution, the researchers tracked how the system absorbed energy over up to 1,000 driving cycles.

The measurements revealed that the system does not heat up immediately. Instead, it enters a prethermal plateau, during which entropy and particle imbalance remain nearly constant before rapid heating sets in. The lifetime of this plateau was found to be doubly tunable and followed a clear power-law dependence on the driving frequency with the universal scaling exponent 2n+ 1, linking the heating timescale directly to the structure of the random drive.

Further analysis showed that, at later times, entanglement spreads across the system and obeys a strong volume-law scaling. In this regime, commonly used classical simulation methods, including tensor-network approaches, fail to reproduce the observed dynamics, highlighting the complexity of the heating process in large driven quantum systems.

By directly tracking heating dynamics under random multipolar driving, this work establishes an experimental framework for studying thermalization beyond periodic and quasiperiodic protocols. The observation of a tunable prethermal plateau and its scaling behavior provides concrete constraints for theoretical descriptions of driven many-body systems. At the same time, the emergence of volume-law entanglement at later times highlights the growing gap between experimental quantum simulators and classical numerical approaches in modeling long-time non-equilibrium dynamics.

This study entitled "Prethermalization by random multipolar driving on a 78-qubit processor" was published on Nature.

The study was supported by the National Natural Science Foundation of China, the Innovation Program for Quantum Science and Technology, the Beijing Nova Program, the Natural Science Foundation of Guangdong Province, and the China Postdoctoral Science Foundation.

Fig.1 Quantum processor and experimental scheme. (Image by Institute of Physics)

Fig.2 Prethermalization by random multipolar driving (RMD) in an 8-qubit system. (Image by Institute of Physics)

Fig.3 Scaling behavior of the prethermal lifetime with driving frequency. (Image by Institute of Physics)

Fig.4 Entanglement dynamics and volume-law scaling. (Image by Institute of Physics)

Contact:
Institute of Physics
Heng Fan
Email：hfan@iphy.ac.cn

Key words:
Quantum simulation; Quantum thermalization; Superconducting qubits.

Abstract:
Chinese scientists observed a tunable prethermal plateau in a 78-qubit quantum processor, showing how random multipolar driving controls the system’s heating before full thermalization.