Observation of Superconducting Solitons by Terahertz-Light-Driven Persistent Pseudo-Spin Coherence

TL;DR

This paper reports the experimental observation of superconducting solitons in an iron-based superconductor driven by intense terahertz light, revealing a new way to control quantum coherence for advanced quantum technologies.

Contribution

It demonstrates the first experimental realization of driven superconducting solitons and elucidates their dynamics using quantum kinetic simulations, introducing a novel method for coherent control in superconductors.

Findings

Observation of Floquet-like spectral sidebands indicating soliton formation

Resonant enhancement of sidebands with temperature and field strength

Corroboration of synchronized pseudo-spin oscillations via simulations

Abstract

Overcoming the decoherence bottleneck remains a central challenge for advancing coherent superconducting quantum device and information technologies. Solitons -- non-dispersive wave packets stabilized by the collective synchronization of quantum excitations -- offer a robust pathway to mitigating dephasing, yet their realization in superconductors has remained experimentally elusive. Here, we report the observation of a driven soliton state in epitaxial thin films of an iron-based superconductor (Co-doped BaFe$_2$As$_2$), induced by intense, multi-cycle terahertz (THz) periodic driving. The dynamical transition to this soliton state is marked by the emergence of Floquet-like spectral sidebands that exhibit a strongly nonlinear dependence on THz laser field strength and a resonant enhancement with temperature. Quantum kinetic simulations corroborate these observations, allowing us to underpin the emergence of synchronized Anderson pseudo-spin oscillations -- analogous to Dicke superradiance -- mediated by persistent order parameter oscillations. In this coherently driven state, the observed sidebands result from difference-frequency mixing between the THz drive and persistent soliton dynamics. These findings establish a robust framework for coherently driving and controlling superconducting soliton time-crystal-like phases using low dissipation, time-periodic THz fields, enabling prospects for THz-speed quantum gate operations, long-lived quantum memory, and robust quantum sensing based on enhanced macroscopic pseudo-spin coherence.