Unveiling the spin-singlet states of two electron-hole pair complexes using two-photon excitation in a GaAs/AlAs quantum dot

The ability to initialize excitonic states in the high-energy orbital levels of quantum dots provides additional degrees freedom for all-optical spin-driving protocols. Here, authors show that unconventional two-photon excitation can simultaneously photocreate two electron-hole pairs located on distinct a GaAs dot. Tuning laser energy allows triplet and singlet spin biexciton be selectively addressed. measured radiative cascades suggest importance many-body effects these weakly confined dots.