Study of Nucleation Phenomena in ^3He-^4He Liquid Mixtures-Quantum Nucleation-

量子成核是一种宏观的量子隧穿现象，伴随着亚稳态系统的衰变，用宏观变量来描述。量子成核的概念目前应用于物理学的各个领域。因此，获取这一现象的确凿证据就显得尤为重要。我们首次系统地研究了低温相分离动力学，在低至0.4mK的双组分亚稳体系中作为过饱和液体^3He-^4He的稀相混合物。实验确定了临界过饱和度，DELTAchi3， cr随温度从0.4mK到160mK的变化。其中，DELTAchi3， cr为稀相的^3He浓度偏离平衡值的上限。在约10mK以下，DELTAchi3的值cr几乎与温度无关。这一事实强烈表明，相分离是由量子成核引发的，至少在这个温度区域是如此。我们的结果的另一个有趣的特征是，DELTAchi3， cr随着温度超过10mK而增加。这与从量子到经典状态的交叉考虑的简单期望相冲突。通过考虑耗散对隧穿概率的影响，可以定性地理解这种行为。在理论方面，我们重新检验了宏观量子成核的Lifshitz-Kagan模型。结果表明，苔藓的R依赖性对成核速率有深远的影响。这里，R是虚核的半径。我们给出了一个从广义非线性薛定谔场模型推导出Lifshitz-Kagan模型的草图。

Quantum nucleation is a kind of macroscopic quantum tunneling phenomena, accompanying the decay of metastable system described with a macroscopic variable. The concept of quantum nucleation is currently used in varioious fields of physics. So it is extremely important to obtain the corroborative evidence of the phenomenon.We made the first systematic studies of the low temperature phase-separation kinetics, down to 0.4mK in the two-component metastable system as a supersaturated liquid^3He-^4He mixture of dilute phase. The experiments determined the values of critical supersaturation, DELTAchi3, cr, as a function of temperature from 0.4mK up to 160mK.Here, DELTAchi3, cr, is the upperlimit of the deviation of ^3He concentration of dilute phase from the equilibrium value. The values of DELTAchi3, cr, becomes almost independent of temperature below about 10mK.This fact strongly suggests that the phase-separation is triggered by quantum nucleation, at least in this temperature region.Another interesting feature of our results is that DELTAchi3, cr, increases with temperature above about 10mK.This conflicts with a simple expectation of the crossover consideration from the quantum to the classical regime. Such behavior may qualitatively be understood by taking into account the effect of dissipation on the tunneling probability.In theoretical side, we re-examined the Lifshitz-Kagan model of macroscopic quantum nucleation. It is shown that the R dependence of the moss has a profound effect on the nucleation rate. Here, R is radius of the virtual nucleus. We gave a sketch to deduce the Lifshitz-Kagan model from a generalized non-linear Schrodinger field model.