Bose-Einstein Condensation Measurements and Superflow in Condensed Helium
Bose-Einstein Condensation Measurements and Superflow in Condensed Helium
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玻色-爱因斯坦凝聚测量和凝聚氦中的超流
DOI：
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发表时间：
2013
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通讯作者：
H. Glyde
中科院分区：
文献类型：
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作者：
H. Glyde
本文综述了液态氦和固态氦中玻色-爱因斯坦凝聚（BEC）的描述和测量。BEC定义为玻色气体，随后通过对均匀和非均匀系统都有效的单体密度矩阵（OBDM）相互作用系统。建立了BEC产生的相位相干性与超流之间的联系。最近的测量表明，液态4 He中的冷凝物分数从饱和蒸气压（p = 0）下的7.25± 0.75%下降到接近凝固压力（p=25.3 bar）的压力p=24 bar下的2.8± 0.2%。外推到固体密度表明固体中的冷凝物分数为1%或更少，假设冻结的液体结构如无定形固体。结晶固体中的测量未能检测到上限设定为n 0 ≤ 0.3%的冷凝物。机会直接观察BEC在液体4 He局限于多孔介质中，BEC是本地化的补丁无序，并在无定形固体氦进行了讨论。
We review the formulation and measurement of Bose-Einstein condensation (BEC) in liquid and solid helium. BEC is defined for a Bose gas and subsequently for interacting systems via the one-body density matrix (OBDM) valid for both uniform and non-uniform systems. The connection between the phase coherence created by BEC and superflow is made. Recent measurements show that the condensate fraction in liquid 4He drops from 7.25±0.75 % at saturated vapor pressure (p≈0) to 2.8±0.2 % at pressure p=24 bars near the solidification pressure (p=25.3 bar). Extrapolation to solid densities suggests a condensate fraction in the solid of 1 % or less, assuming a frozen liquid structure such as an amorphous solid. Measurements in the crystalline solid have not been able to detect a condensate with an upper limit set at n0≤0.3 %. Opportunities to observe BEC directly in liquid 4He confined in porous media, where BEC is localized to patches by disorder, and in amorphous solid helium is discussed.