Ultrasonic light storage in a quantum well: A photon assembly line

Surface acoustic waves are used to effectively convert photogenerated excitons in a piezoelectric semiconductor quantum well into long-lived electron–hole polarizations. The strong lateral piezoelectric fields ionize the excitons and spatially separate the resulting electrons and holes. The strongly reduced wave function overlap results in very long storage times for this polarization which propagates across the sample at the speed of sound. External and deliberate screening of the piezoelectric fields triggers radiative recombination after long delay times and at a remote location of the sample.