Coherent generation and interference of excitons and biexcitons in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells

We report measurements of two-photon transitions to the biexciton state and exciton-biexciton transitions (M band) in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As multiple quantum wells by spectrally resolving the self-diffraction in a four-wave-mixing experiment. Furthermore, nonlinear quantum beats between a coherently prepared population of excitons and biexcitons are observed. The analysis yields a binding energy of 1.8 meV for the biexciton in 116-Å quantum wells.