We study sound in a single-channel one-dimensional quantum liquid. In contrast to classical fluids, instead of a single sound mode we find two modes of density oscillations. The speeds at which these two sound modes propagate are nearly equal, with the difference that scales linearly with the small temperature of the system. The two sound modes emerge as hybrids of the first and second sounds, and combine oscillations of both density and entropy of the liquid.

中文翻译：

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一维量子液体中的混合声模

我们研究单通道一维量子液体中的声音。与经典流体相比，我们发现了两种密度振荡模式，而不是单一的声音模式。这两种声音模式传播的速度几乎相等，其差异随系统温度的降低呈线性比例。这两种声音模式是第一声音和第二声音的混合，并结合了液体的密度和熵的振动。