Femtosecond dynamics of excitons under extreme magnetic confinement

The resonant optical nonlinearities of GaAs/AlGaAs quantum wells are measured with femtosecond time resolution, as the quasi-two-dimensional states are further confined into quasizero dimensions by a perpendicular magnetic field. We apply fields up to 12 T to demonstrate that exciton-exciton Coulomb interactions are strongly modified by quasi-zero dimensional confinement, in agreement with many-body theory. These measurements demonstrate for the first time the remarkable result that at high magnetic fields an ensemble of 1s, electron-hole pairs behaves like a gas of noninteracting particles.