Phonon stability and sound velocity of quantum droplets in a boson mixture
Phonon stability and sound velocity of quantum droplets in a boson mixture
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DOI：
10.1103/physrevb.102.220503
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发表时间：
2020-12-14
影响因子：
3.7
通讯作者：
Yin, Lan
中科院分区：
文献类型：
--
作者：
Gu, Qi;Yin, Lan
在二元玻色子混合物和偶极玻色气体的实验中已经实现了量子液滴。在这些系统中，玻色-爱因斯坦凝聚的平均场能量是有吸引力的，而排斥性的李黄阳能量对稳定性至关重要。然而，由于在构造Bogoliubov哈密顿量时没有考虑Lee-Huang-Yang项，因此在液滴状态下，人们面临着声子模动态不稳定的问题。在这项工作中，我们超越了Bogoliubov理论，研究了双玻色子混合物的量子液滴中声子模式是如何稳定的。与Beliaev对单组分玻色气体的方法类似，我们计算了玻色子传播子自能的高阶贡献。我们发现自旋和声子激发之间的相互作用是声子稳定的关键。我们在实验中通过测量液滴的超流体临界速度得到了可以测试的声速。讨论了该量子液滴的贝氏阻尼。
Quantum droplets have been realized in experiments on binary boson mixtures and dipolar Bose gases. In these systems, the mean-field energy of the Bose-Einstein condensation is attractive, and the repulsive Lee-HuangYang energy is crucial for stability. However, since the Lee-Huang-Yang term is not taken into account when constructing the Bogoliubov Hamiltonian, in the droplet regime one faces the problem of dynamically unstable phonon modes. In this work, we go beyond the Bogoliubov theory to study how the phonon mode is stabilized in the quantum droplet of a binary boson mixture. Similar to Beliaev's approach to a single-component Bose gas, we compute higher-order contributions to the self-energy of the boson propagator. We find that the interaction between spin and phonon excitations is the key for the phonon stability. We obtain the sound velocity which can be tested by measuring the superfluid critical velocity of the droplet in experiments. Beliaev damping of this quantum droplet is also discussed.