Coherently pumped (Kerr) solitons in an ideal optical microcavity are expected to undergo random quantum motion that determines fundamental performance limits in applications of the soliton microcombs¹. Here this random walk and its impact on Kerr soliton timing jitter are studied experimentally. The quantum limit is discerned by measuring the relative position of counter-propagating solitons². Their relative motion features weak interactions and also presents common-mode suppression of technical noise, which typically hides the quantum fluctuations. This is in contrast to co-propagating solitons, which are found to have relative timing jitter well below the quantum limit of a single soliton on account of strong correlation of their mutual motion. Good agreement is found between theory and experiment. The results establish the fundamental limits to timing jitter in soliton microcombs and provide new insights on multisoliton physics.

理想光学微腔中的相干泵浦 (Kerr) 孤子预计会经历随机量子运动，这决定了孤子微梳¹应用中的基本性能限制。这里通过实验研究了这种随机游走及其对克尔孤子时序抖动的影响。通过测量反向传播孤子的相对位置来识别量子极限². 它们的相对运动具有弱相互作用，并且还呈现出技术噪声的共模抑制，这通常隐藏了量子涨落。这与共同传播的孤子形成对比，由于它们相互运动的强相关性，它们被发现具有远低于单个孤子的量子极限的相对时间抖动。在理论和实验之间找到了很好的一致性。结果确定了孤子微梳中时序抖动的基本限制，并为多孤子物理学提供了新的见解。