Novel Quantum\nStates of Exciton–Floquet Composites:\nElectron–Hole Entanglement and Information

Coulomb exchange between distinct electron–hole\nmodes, i.e.,\nexciton and Floquet states, in two-dimensional semiconductors is explored.\nCoherent ultrafast mixing of the exciton and Floquet states under\nweak optical pumping is investigated through a theoretical description\nof time-resolved and angle-resolved photoemission spectroscopy (tr-ARPES)\nin an extended Haldane model that includes the electron–hole\nCoulomb interaction. Two branches of novel quantum states are found\nin the form of bosonic exciton–Floquet composites, which result\nfrom exchange coupling due to the Coulomb interaction. Furthermore,\ntr-ARPES could be directly employed for the density matrix element\nof the biparticle subsystem of photoelectron and hole, and electron–hole\nentanglement and information could be further explored. This finding\nsuggests a unique platform to study the buildup and dephasing of novel\nexciton–Floquet composites and to resolve the information carried\nby them, which would enable the pursuit of new reconfigurable devices\nbased on two-dimensional semiconductors.