Coherent control of terahertz charge oscillations in a coupled quantum well using phase-locked optical pulses

We demonstrate that we can enhance, weaken, and also phase shift terahertz (THz) radiation emitted by optically excited quantum beats in a coupled quantum well. The changes in the evolution of the THz radiation are induced by exciting the sample with a second optical pulse, phase locked with the first. We observe phase shifts in the emitted THz radiation of 330 fs for a change in the optical-pulse separation of only 1.33 fs.