近日，美国新墨西哥大学的John B. DeBrota及其研究团队取得一项新进展。经过不懈努力，他们提出QBism对量子动力学和退相干的解释。相关研究成果已于2024年11月6日在国际知名学术期刊《物理评论A》上发表。

该研究团队基于范·弗拉森的反射原则提出一个表示定理来回答这些问题。简而言之，主体对量子动力学的赋值代表了她相信自己所考虑的测量行动不会改变她对未来赌局的当前赔率。这一方法的推论是，人们可以理解“开放系统动力学”，而无需引入“具有测量记录的环境”，这是量子测量退相干解释中常见的做法。

相反，QBism的理解更根本地基于主体对感兴趣系统（而非系统加环境）的信念，以及她对可能对该系统进行的测量的判断。更广泛地看，这一结果确立了QBism的主张，即测量本身是量子理论的核心概念，也是任何未来QBism本体论必须依赖的框架。

据悉，量子贝叶斯理论（QBism）长期以来认识到，量子态、正算子值测量元素、Kraus算子乃至幺正运算都属于同一类型：它们表达了主体关于其对外部世界可能采取的行动所带来的后果（对主体自身而言）的信念体系的不同方面。这种行动-后果对在传统上被称为“量子测量”。

当将这一概念应用于测量时，量子理论的计算就被视为对贝叶斯决策理论的一种基于经验的补充。这种激进的方法使QBism得以消除了困扰量子力学其他解释的概念问题。然而，一个问题始终悬而未决：如果QBism不相信存在一个随时间演化的本体论（与主体无关）动力学变量，那么在不进行测量的情况下，为何会对她的量子态赋值存在任何约束？她为何会引入幺正或开放系统的量子动力学？

附：英文原文

Title: QBism's account of quantum dynamics and decoherence

Author: John B. DeBrota, Christopher A. Fuchs, Rüdiger Schack

Issue&Volume: 2024/11/06

Abstract: QBism has long recognized quantum states, positive-operator-valued measure elements, Kraus operators, and even unitary operations to be of the same type: they express aspects of an agent's belief system concerning the consequences (for her) of actions she might take upon her external world. Such action-consequence pairs have conventionally been called “quantum measurements.” The calculus of quantum theory is then viewed as an empirically motivated addition to Bayesian decision theory when brought to this notion of measurement. This radical approach has allowed QBism to eliminate conceptual problems that plague other interpretations of quantum mechanics. However, one issue has remained elusive: If a QBist does not believe in the existence of an ontic (agent-independent) dynamical variable evolving over time, why would there be any constraints on her quantum-state assignment in the absence of performing a measurement ？Why would she introduce unitary or open-system quantum dynamics at all？ Here, we present a representation theorem based on van Fraassen's reflection principle to answer these questions. Simply put, an agent's assignment of quantum dynamics represents her belief that a measurement action she is contemplating would not change her current odds for future gambles. A corollary to this approach is that one can make sense of “open-system dynamics” without the need to introduce an “environment with a measurement record,” as is common in decoherence accounts of quantum measurement. QBism's understanding instead rests more fundamentally on an agent's beliefs about the system of interest (not system plus environment) and her judgments about measurements she might perform on that system. More broadly, this result establishes QBism's contention that measurement itself is the central concept of quantum theory and thus the framework upon which any future QBist ontology must hang.

DOI: 10.1103/PhysRevA.110.052205

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.110.052205