Quantum Beating Induced by Subcycle Terahertz Supercurrent Driving

Recent studies have shown that time-periodic acceleration of superconducting condensates driven by oscillating terahertz (THz) fields generates a superfluid center-of-mass momentum that persists long after the driving pulse has passed [1,2]. An effective electromagnetic field—distinct from the bare THz field—emerges from the interplay between the applied field and the induced supercurrent. Understanding how this effective field breaks equilibrium symmetry on sub-cycle timescales and enables quantum beating between driven states is of fundamental importance. Here, we directly visualize the sub-cycle acceleration of the superconducting condensate, revealing the buildup of quantum beating within individual oscillation periods. This lightwave current acceleration mechanism provides a pathway toward sub-cycle control of dissipationless topological currents and other anomalous quantum transport phenomena.

[1] X. Yang, et al., Nature Photonics 13, 707 (2019).

[2] C. Vaswani, et al., Physical Review Letters, 124, 207003 (2020).