膨胀和收缩冷原子宇宙中哈勃衰减和放大的精确测定
Accurate Determination of Hubble Attenuation and Amplification in Expanding and Contracting Cold-Atom Universes
摘要：
在膨胀的宇宙中，相对论性的标量场被认为会被“哈勃摩擦”所衰减，这是由基础时空度规的膨胀引起的。相反，在收缩的宇宙中，这种伪摩擦会导致放大。在这里，我们实验测量五倍更好的精度，哈勃衰减和放大的膨胀和收缩环形玻色-爱因斯坦凝聚体，其中声子类似于宇宙学的标量场。我们发现，所观察到的衰减或放大依赖于声子场的时间相位，这是唯一可能的非绝热动力学。哈勃摩擦力的测量强度与最近的理论不一致[J. M。Gomez Llorente和J. Plata，{ \it Phys. Rev. A} { \bf 100} 043613（2019）和S. Eckel和T.雅各布森，{ \it SciPost Phys.} { \bf 10} 64（2021）];因为我们的实验探测了这个理论范围之外的物理学-在中等厚度的环中具有大的激发-这表明了新物理学的存在。
英文摘要：
In the expanding universe, relativistic scalar fields are thought to be attenuated by "Hubble friction", which results from the dilation of the underlying spacetime metric. By contrast, in a contracting universe this pseudo-friction would lead to amplification. Here, we experimentally measure with five-fold better accuracy, both Hubble attenuation and amplification in expanding and contracting toroidally-shaped Bose-Einstein condensates, in which phonons are analogous to cosmological scalar fields. We find that the observed attenuation or amplification depends on the temporal phase of the phonon field, which is only possible for non-adiabatic dynamics. The measured strength of the Hubble friction disagrees with recent theory [J. M. Gomez Llorente and J. Plata, {\it Phys. Rev. A} {\bf 100} 043613 (2019) and S. Eckel and T. Jacobson, {\it SciPost Phys.} {\bf 10} 64 (2021)]; because our experiment probes physics outside the scope of this theory -- with large excitations in rings of intermediate thickness -- this indicates the presence of new physics.
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