Novel Quantum States of Exciton–Floquet Composites: Electron–Hole Entanglement and Information

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