Coherent control of biexciton waves in highly degenerate regime

Summary form only given. We demonstrate the generation of biexcitons with a small momentum spread in CuCl by the phase matched two polariton absorption, using femtosecond pulses from conventional mode locked Ti:sapphire laser. We create biexciton ensemble in supercooled state with a phase space density of about 10/sup 7/ at an excitation density of 4 /spl mu/J/cm/sup 2//pulse. Such highly degenerate biexcitons behave as macroscopic coherent waves with a coherence time governed by their lifetime. The coherent wave nature of biexcitons can be observed by studying the interference between two biexciton waves created at different times. The results are shown of biexciton wave interference probed by four wave mixing signals. The high visibility of the interference fringes indicates that the normalized correlation term is as high as 0.98. The role of the nonlinearities arising from saturation and biexciton repulsion is discussed in turns of GP equation which describes the temporal evolution of weakly interacting highly degenerate bosons.