Driven systems are of fundamental scientific interest, as they can exhibit properties distinct from the same system at equilibrium. In certain cases, long-lived states of driven matter can emerge with new material properties. Here we probe the excitation spectrum of an emergent patterned state in a driven superfluid and find that its response is identical to that of a one-dimensional supersolid. By preparing wave packets as well as specific collective modes and probing their dynamics, we identify two distinct sound modes associated with spontaneously broken U(1) and translational symmetries. Consistent with the hydrodynamic description of superfluid smectics, longitudinal excitations propagate with finite velocities, whereas transverse perturbations exhibit diffusive behaviour. These results demonstrate how the conceptual framework of supersolidity can be used to characterize dynamic and far-from-equilibrium states.

驱动系统具有基本的科学价值，因为它们在平衡时可以表现出与同一系统不同的特性。在某些情况下，驱动物质的长期状态可能会随着新的材料属性而出现。在这里，我们探测了驱动超流体中新兴模式态的激发光谱，发现它的响应与一维超固体的响应相同。通过准备波包以及特定的集体模式并探测它们的动态，我们确定了与自发断开的 U（1） 和平移对称性相关的两种不同的声音模式。与超流体语义的流体动力学描述一致，纵向激励以有限速度传播，而横向扰动表现出扩散行为。这些结果证明了如何使用超固体的概念框架来表征动态和远非平衡状态。