Quantum coherence tomography of light-controlled superconductivity

Abstract The coupling between superconductors and oscillation cycles of light pulses, i.e., lightwave engineering, is an emerging control concept for superconducting quantum electronics. Although progress has been made towards terahertz-driven superconductivity supercurrents, the interactions able to drive non-equilibrium pairing are still poorly understood, partially due lack measurements high-order correlation functions. In particular, sensing exotic collective modes that would uniquely characterize light-driven coherence, in a way analogous Meissner effect, very challenging but much needed. Here we report discovery parametrically driven by light-induced order-parameter oscillations iron-based superconductors. time-periodic relative phase dynamics coupled electron hole bands drives transition distinct parametric state out-of-equalibrium. This emergent coherence characterized unique phase–amplitude mode with Floquet-like sidebands at twice Higgs frequency. We measure non-perturbative, correlations this separating terahertz-frequency multidimensional coherent spectra into pump–probe, bi-Higgs frequency sideband peaks. find higher-order dominate above critical field, which indicates breakdown susceptibility perturbative expansion matter.