To store or process information encoded as light signals, it is often necessary to slow down strings of photons.A group of scientists from the University of Munich has developed a semiconductor device that serves as a quantum well, which incorporates a thin film of indium gallium arsenide sandwiched between layers of gallium arsenide.When photons enter the quantum well, they are temporarily converted into electrons. A pulsed acoustic wave sent into the well slows the electrons for a few microseconds. This technique could lead to advances in beam steering, multiplexing and demultiplexing of optical signals on a single chip.