We discuss the transport of a tracer particle through the Bosea€“Einstein condensate of a Bose gas. The particle interacts with the atoms in the Bose gas through two-body interactions. In the limiting regime where the particle is very heavy and the Bose gas is very dense, but very weakly interacting (a€?mean-???eld limita€?), the dynamics of this system corresponds to classical Hamiltonian dynamics. We show that, in this limit, the particle is decelerated by emission of gapless modes into the condensate (Cerenkov radiation). For an ideal gas, the particle eventually comes to rest. In an interacting Bose gas, the particle is decelerated until its speed equals the propagation speed of the Goldstone modes of the condensate. This is a model of a€?Hamiltonian frictiona€?. It is also of interest in connection with the phenomenon of a€?decoherencea€? in quantum mechanics. This note is based on work we have carried out in collaboration with D Egli, I M Sigal and A Soffer.
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机译：我们讨论了示踪剂粒子通过玻色气体的Bosea-Einstein冷凝物的传输。粒子通过两体相互作用与玻色气体中的原子相互作用。在粒子非常重且玻色气体非常稠密但相互作用非常弱的极限状态下（均值-极限极限），该系统的动力学与经典的哈密顿动力学相对应。我们证明，在此极限下，粒子通过将无间隙模式发射到冷凝物中而被减速（塞伦科夫辐射）。对于理想的气体，粒子最终会静止。在相互作用的Bose气体中，粒子减速直至其速度等于凝结水的Goldstone模的传播速度。这是“哈密顿摩擦”的模型。与“退相干”现象有关的兴趣也很重要。在量子力学中。本说明基于我们与D Egli，I M Sigal和A Soffer合作进行的工作。
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