A new spectroscopy to unravel spin states in GaAs/AlAs quantum dots

The on-demand generation of entangled photons is an essential achievement leading to important applications for quantum technologies. In semiconductor quantum dots (QDs), the radiative biexciton-exciton cascade is successfully employed. Resonant two-photon excitation (TPE), coherently preparing the biexcitonic state, significantly improves the entangled photon-pairs emission rate.

Members of INSP have found a novel use of this technique (TPE) to resonantly probe the spin properties of excited biexcitonic states – impossible to be detected by more conventional techniques – where the two electron-hole (e-h) pairs occupy distinct orbital levels.

(a) Level diagram representing the resonant 2-photon excitation between the exciton and the biexciton. Both “conduction-valence” R_c-vand “atomic” notation R_atom. are used to represent these quasi-particles to improve clarity.

(b) Luminescence spectrum showing the experimental implementation of the resonant 2-photon excitation. The insert magnifies the luminescence from the p_c-p_v excited levels, where the doublet appears.

(c) Luminescence intensity of one of the triplet states as a function of the laser energy.