Small particles can have an angular momentum that points in a certain direction — the spin. This spin can be manipulated by a magnetic field. This principle, for example, is the basic idea behind magnetic resonance imaging as used in hospitals. An international research team has now discovered a surprising effect in a system that is particularly well suited for processing quantum information: the spins of phosphorus atoms in a piece of silicon, coupled to a microwave resonator. If these spins are cleverly excited with microwave pulses, a so-called spin echo signal can be detected after a certain time — the injected pulse signal is re-emitted as a quantum echo. Surprisingly, this spin echo does not occur only once, but a whole series of echoes can be detected. This opens up new possibilities of how information can be processed with quantum systems.
The experiments were carried out at the Walther-Meissner-Institute