自发对称性破缺后无量子涨落的判据
Criteria for the absence of quantum fluctuations after spontaneous symmetry breaking
摘要：
对称性自发破缺的宏观最低能量状态，是一个非常稳定的波包，其中心在对称空间中自发选择的经典方向。然而，对于海森堡铁磁体，量子基态正是经典基态。这与铁磁体的其他特殊性质相吻合，包括自发的时间反演对称性破缺，Nambu-Goldstone模式的数量减少以及没有薄光谱（安德森状态塔）。最近发现的其他非相对论性系统较少的南武-戈德斯通模式表明，这些特点也适用于那里。我建立了量子涨落和其他所有特征不存在的精确标准。特别地，序参量与哈密尔顿算子可交换是不够的。它导致了一个可测量的更大的相干时间的叠加在小，但宏观系统。
英文摘要：
The lowest-energy state of a macroscopic in which symmetry is spontaneously broken, is a very stable wavepacket centered around a spontaneously chosen, classical direction in symmetry space. However, for a Heisenberg ferromagnet the quantum groundstate is exactly the classical groundstate. This coincides with other exceptional properties of the ferromagnet, including spontaneous time-reversal symmetry breaking, a reduced number of Nambu-Goldstone modes and the absence of a thin spectrum (Anderson tower of states). Recent discoveries of other non-relativistic systems with fewer Nambu-Goldstone modes suggest these specialties apply there as well. I establish precise criteria for the absence of quantum fluctuations and all the other features. In particular, it is not sufficient that the order parameter commute with the Hamiltonian. It leads to a measurably larger coherence time of superpositions in small but macroscopic systems.
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