Science 361, 57–60 (2018)

The building blocks of quantum circuits, such as single-photon transistors and switches, are key elements for next-generation information technology. However, realizing such structures for compact solid-state devices is challenging, because they require highly efficient photon–memory interaction and broad bandwidths at optical frequencies, along with high switching rates. Only some of these criteria have been achieved so far with alternative approaches such as atomic traps. Now, Shuo Sun and colleagues have successfully demonstrated a fully functional device experimentally.

Sun et al. took a nanophotonic cavity and embedded a charged quantum dot in it, loaded with a single electron. When subjected to a magnetic field, the system performed as a semiconductor qubit, in which two spin configurations represent a stable quantum memory. They demonstrated that the quantum memory could be activated by a single gate photon, and then transmitted a signal field of a specific number of photons in only a few tens of picoseconds.