复旦大学王靖团队近日研究了量子非局部不稳定性。相关论文于2025年5月27日发表在《物理评论A》杂志上。

量子纠缠和量子不稳定性是表征量子态不同方面的基本资源：纠缠反映了非局域相关性，而不稳定性量化了与稳定态的偏差。只有当两个量都存在时，量子态才成为通用量子计算等应用的宝贵资源。研究组提出量子非局域不稳定性（NN）是衡量这种组合资源的有效指标，结合了纠缠和不稳定性。他们证明了神经网络可以精确计算两个量子比特纯态，与纠缠谱建立了直接关系。然后，将神经网络的定义扩展到混合态，并探索它在多体量子系统中的存在。 

研究组揭示了两点神经网络在临界状态下根据幂律衰减，表明它可以作为相变的有效量子信息探针。此外，还探索了测量诱导的神经网络，并发现了一个有趣的现象，称为“不稳定性交换”，其中测量后的神经网络的衰减速度比任何测量前的相关性都慢。这种现象的发生为纠缠交换和非平凡符号结构的存在提供了充分条件。因此，该研究结果代表了准确量化状态“定量性”的关键一步，并从多个角度对神经网络的特性进行了深入了解。

附：英文原文

Title: Quantum nonlocal nonstabilizerness

Author: Dongheng Qian, Jing Wang

Issue&Volume: 2025/05/27

Abstract: Quantum entanglement and quantum nonstabilizerness are fundamental resources that characterize distinct aspects of a quantum state: Entanglement reflects nonlocal correlations, while nonstabilizerness quantifies the deviation from stabilizer states. A quantum state becomes a valuable resource for applications like universal quantum computation only when both quantities are present. Here, we propose that quantum nonlocal nonstabilizerness (NN) serves as an effective measure of this combined resource, incorporating both entanglement and nonstabilizerness. We demonstrate that NN can be precisely computed for two-qubit pure states, establishing a direct relationship with the entanglement spectrum. We then extend the definition of NN to mixed states and explore its presence in many-body quantum systems. We reveal that the two-point NN decays according to a power law in critical states, indicating that it can serve as an effective quantum information probe for phase transitions. Furthermore, we explore measurement-induced NN and uncover an intriguing phenomenon termed “nonstabilizerness swapping,” wherein post-measurement NN decays more slowly than any pre-measurement correlations. The occurrence of this phenomenon provides a sufficient condition for both entanglement swapping and the presence of a nontrivial sign structure. Our results thus represent a pivotal step toward accurately quantifying the “quantumness” of a state and bring insights from multiple perspectives to the property of NN.

DOI: 10.1103/PhysRevA.111.052443

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.111.052443