量子相变是指发生在绝对零度的相变现象。与热相变不同的是，热相变的发生是由于热扰动所造成，而量子相变是经由量子涨落所造成。量子相变的发生代表着在量子多体系统中基态的性质随着外部参数发生突然的骤变。传统上研究量子相变的方法和研究热相变的方法类似，主要根据朗道的对称破缺理论和序参量来决定量子系统的相图。近年来由于量子信息学的蓬勃发展，有一些物理学家利用量子信息学来研究量子相变，例如纠缠熵和保真度。

In physics, a quantum phase transition (QPT) is a phase transition between different quantum phases (phases of matter at zero temperature). Contrary to classical phase transitions, quantum phase transitions can only be accessed by varying a physical parameter—such as magnetic field or pressure—at absolute zero temperature. The transition describes an abrupt change in the ground state of a many-body system due to its quantum fluctuations. Such a quantum phase transition can be a second-order phase transition.