We explain our method of creating an in-plane harmonic potential for indirect excitons in coupled quantum wells, which has been developed for experiments on Bose condensation of excitons in two dimensions, although this method may also be used for trapping a two-dimensional electron gas. The indirect excitons in our coupled quantum wells exhibit a Stark shift of over 60 meV and lifetime of approximately 100 ns when electric field is applied normal to the wells. The excitons also move in response to applied voltage as if they had charge, with an effective mobility of 800 cm 2 /V s. We find that the effects of screening of the electric field at high carrier density are very important for understanding the behavior of the excitons.

We have demonstrated a method of using inhomogeneous stress to create an in-plane harmonic potential in GaAs quantum wells which works equally well for excitons and for free conduction electrons. The depth of the well can be continuously varied via an external control. This essentially provides a type of gate for controlling the motion of carriers, e.g., a two-dimensional electron gas, without using electric field.

We have measured the Auger recombination rate for excitons in Cu 2 O trapped in harmonic potential wells created by inhomogeneous stress. The rate is higher than assumed in most previous experiments, but consistent with the rate reported recently by O'Hara et al. ͓Phys. Rev. B ͑to be published͔͒. We find that even given this rate, the orthoexciton density immediately after creation in the well by a short laser pulse may be high enough for Bose condensation, and there is some evidence that this may occur.

We measure a dynamical blueshift of the indirect exciton in GaAs-coupled quantum wells of over 20 meV for carrier densities in the range 10 9 -10 12 cm Ϫ2 . We show that this shift is a many-body effect, which is proportional to the indirect exciton density over a broad range of densities, and it is accompanied by homogeneous broadening, which is proportional to the indirect exciton density.

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