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This study introduces a novel paradigm for achieving widely tunable many-body Fano quantum interference in low-dimensional semiconducting nanostructures, beyond the conventional requirement of closely matched energy levels between discrete and continuum states observed in atomic Fano systems. Leveraging Floquet engineering, we demonstrate remarkable tunability of Fano lineshapes, even when the original discrete and continuum states are separated by over 1 eV. Specifically, by controlling the quantum pathways of discrete phonon Raman scattering using femtosecond laser pulses, we tune the Raman intermediate states across the excitonic Floquet band. This manipulation yields continuous transitions of Fano lineshapes from antiresonance to dispersive and to symmetric Lorentzian profiles, accompanied by significant variations in Fano parameter 𝑞 and Raman intensity spanning two orders of magnitude. We further show that a subtle shift in the excitonic Floquet resonance, achieved by controlling the intensity of the femtosecond laser,
profoundly modifies quantum interference strength from destructive to constructive interference. Our study reveals the crucial roles of Floquet engineering in coherent light-matter interactions, and opens up new avenues for coherent control of Fano quantum interference over broad energy spectrum in low-dimensional semiconducting nanostructures

We demonstrate that driving the phonon and excitonic excitations by femtosecond laser can profoundly modify the Fano quantum interference: it eliminates the conventional requirement of closely matched energy levels between the discrete and continuum band of states typically associated with the classical atomic Fano system, and lead to a rich set of quantum interference phenomena within the photon-dressed quantum states. To reveal the optically-controllable many-body Fano effects, we study high-purity M-(6,5) semiconducting single-walled carbon nanotubes (SWCNTs) using energy-dependent pump-probe spectroscopy. We coherently drive the exciton transition and phonon Raman scattering using pump photons at an energy below the one-exciton transition. By systematically tuning the quantum pathways of phonon Raman intermediate states across the resonance of the excitonic Floquet band, we observe the Fano lineshapes evolve continuously from antiresonance to dispersive feature and to symmetric Lorentzian, signifying a shift of interference strength from destructive to constructive interference between the excitonic Floquet state resonance and the phonon Raman intermediate state transition, even when the bare phonon and exciton states are separated by at least 1 eV. We further show that a subtle shift of excitonic Floquet resonance, achieved by controlling the driving pump intensity, can dramatically modify the Fano lineshapes, underscores the ultrasensitive nature of quantum interference on the competing interference pathways. Unlike the conventional Fano resonance, which arises from direct coupling between bare discrete states and continuum band, our results demonstrate the high tunability of Fano quantum interference between excitonic Floquet states and phonon Raman intermediate states, where the quantum pathways of these photon-dressed states can be manipulated by adjusting the intensity and frequency of driving pump. These findings highlight the intricate interplay among photons, electrons and phonons in the low-dimensional nanostructures can offer new avenues for optical manipulation of quantum interference with potential applications in novel quantum optoelectronics and nanodevices. This study has been published on the journal of Advanced Science in August 2024 (DOI).