Virtual-real quantum interference

Summary form only given. We report on the interplay between the virtual polarizations and the real (resonant) polarizations in semiconductors and atoms. Using pulse shaping, pump-probe (PP) and four-wave mixing (FWM), we precisely measure the virtual state amplitude normalized to that of the resonant excitation, and demonstrate in the time domain that indeed, virtual polarizations are 90/spl deg/ out of phase from the resonantly excited polarizations. In our experimental setup, by pulse shaping, we simultaneously excite the real and virtual polarizations and measure their beating. To realize this idea, we performed femto/picosecond nondegenerate FWM and PP in GaAs quantum wells.