AI 中文总结
本研究以光离心机为探针，通过连续驱动克服限制，使分子转子与超流氦进入强耗散耦合机制，实现了对量子流体中分子与热浴耦合强度的直接测量。
AI 中文摘要
超流性的宏观表现为：当物体在液态氦中运动且速度低于朗道临界速度时，所受摩擦力可忽略不计。这种无摩擦运动在纳米尺度如何失效仍是一个未解决的问题。嵌入氦纳米液滴中的分子构成了研究该失效过程的可控系统，但目前尚未有系统达到强耗散耦合机制——即分子向超流的能量转移主导观测到的动力学过程的状态。由短激光脉冲诱导的分子转动是合适的探针，可用于达到旋子能隙范围内的转动能量，超流氦在该范围内支持大量基本激发。然而，旋转分子周围的溶剂化壳层会限制脉冲激发后自由转子可达到的能量，使其远低于旋子激发能量。本研究表明，使用超慢光离心机进行连续驱动可克服这一限制：强场将分子修饰为摆动态，其能量处于超流体集体激发的频谱范围内，使系统进入强耗散机制。由此产生的快速热化过程将分子锁定在旋转场中，直至旋转诱导的能级分裂超过热化速率，之后分子的取向会逐渐消失。本方法可直接测量量子流体中分子与热浴的耦合强度。
英文摘要
A macroscopic manifestation of superfluidity is that objects moving through liquid helium experience negligible friction below the Landau critical velocity. How this frictionless motion breaks down at the nanoscale remains an open question. Molecules embedded in helium nanodroplets represent a well-controlled system for studying this breakdown, yet none has reached the regime of strong dissipative coupling, when energy transfer from the molecule to the superfluid dominates the observed dynamics. Molecular rotation, induced by short laser pulses, offer a suitable probe to reach rotational energies in the range of the roton gap, where superfluid helium supports a large number of elementary excitations. However, the solvation shell around a rotating molecule caps the energy reachable by a free rotor after impulsive excitation well below the roton excitation energy. Here we show that continuous driving with an ultraslow optical centrifuge overcomes this limitation: the strong field dresses the molecule into pendular states whose energies fall within the spectrum of the collective excitations of the superfluid, placing the system in the strong-dissipation regime. The resulting rapid thermalization locks the molecule to the rotating field until the rotation-induced level splittings overtake the thermalization rate, beyond which the molecular alignment is progressively lost. Our approach offers a direct measurement of the molecule-bath coupling in a quantum fluid.
