Transmon platform for quantum computing challenged by chaotic fluctuations

Suppressing chaos with mixed superconducting qubit devices

In quantum information processing, a tension between two different tasks occurs: while qubits' states can be preserved by isolating them, quantum gates can be realized only through qubit-qubit interactions. In arrays of qubits, weak coupling leads to states being spatially localized and strong coupling to delocalized states. Here, we study the average energy level spacing and the relative entropy of the distribution of the level spacings (Kullback-Leibler divergence from Poisson and Gaussian Orthogonal Ensemble) to analyze the crossover between localized and delocalized (chaotic) regimes in li…

Floquet混沌多体系统中的真实量子疤痕

Genuine quantum scars in Floquet chaotic many-body systems

研究揭示了在周期驱动的Floquet多体系统中，量子疤痕与驱动的竞争机制，发现高频极限下Floquet态仍保持疤痕特性，并发现驱动诱导的额外疤痕。

Quantum Chaos and the Correspondence Principle

The correspondence principle is a cornerstone in the entire construction of quantum mechanics. This principle has been recently challenged by the observation of an early-time exponential increase of the out-of-time-ordered correlator (OTOC) in classically non-chaotic systems [E.B. Rozenbaum et al., Phys. Rev. Lett. 125, 014101 (2020)], Here we show that the correspondence principle is restored after a proper treatment of the singular points. Furthermore our results show that the OTOC maintains its role as a diagnostic of chaotic dynamics.

Multi-mode ultra-strong coupling in circuit quantum electrodynamics

With the introduction of superconducting circuits into the field of quantum optics, many novel experimental demonstrations of the quantum physics of an artificial atom coupled to a single-mode light field have been realized. Engineering such quantum systems offers the opportunity to explore extreme regimes of light-matter interaction that are inaccessible with natural systems. For instance the coupling strength $g$ can be increased until it is comparable with the atomic or mode frequency $ω_{a,m}$ and the atom can be coupled to multiple modes which has always challenged our understanding of li…

Quantum correlations as probes of chaos and ergodicity

Long-time average behavior of quantum correlations in a multi-qubit system, collectively modeled as a kicked top, is addressed here. The behavior of dynamical generation of quantum correlations such as entanglement, discord, concurrence, as previously studied, and Bell correlation function and tangle, as identified in this study, is a function of initially localized coherent states. Their long-time average reproduces coarse-grained classical phase space structures of the kicked top which contrast, often starkly, chaotic and regular regions. Apart from providing numerical evidence of such corre…

耗散量子混沌：由随机量子轨迹揭示

Dissipative Quantum Chaos unveiled by Stochastic Quantum Trajectories

本文提出基于随机量子轨迹谱统计的判据，区分开放量子系统的瞬态与稳态混沌，并在驱动-耗散Bose-Hubbard模型和transmon读出中揭示耗散量子混沌现象。

超越非线性电路中的参数驱动强度阈值

Exceeding the Parametric Drive Strength Threshold in Nonlinear Circuits

本文通过实验与数值模拟证明非线性耦合器在强参数驱动下会发生电离并引发混沌动力学，利用瞬时Floquet谱定量表征该现象，为超导量子电路的强驱动限制提供统一理解框架和设计原则。

两类量子混沌：测试 Bohigas-Giannoni-Schmit 猜想的极限

Two types of quantum chaos: testing the limits of the Bohigas-Giannoni-Schmit conjecture

本文区分了本征基混沌与谱混沌两类量子混沌，通过分析泊松哈密顿量系综并利用 Metropolis 算法修改 SYK 模型耦合，发现存在具有本征基混沌而无谱混沌的 $k$-局域哈密顿量，从而指出 ETH 与 RMU 的联系需以 $k$-局域性为前提，挑战了 BGS 猜想。