A burst of ”synchronous” light

Some materials spontaneously emit light if they are excited by an external source, for instance a laser. This phenomenon is known as fluorescence. However, in several gases and quantum systems a much stronger emission of light can occur, when the emitters within an ensemble spontaneously synchronize their quantum mechanical phase with each other and act together when excited. In this way, the resulting light output can be much more intense than the sum of the individual emitters, leading to an ultrafast and bright emission of light – superfluorescence. It only occurs, however, when those emitters fulfill stringent requirements, such as having the same emission energy, high coupling strength to the light field and a long coherence time. As such, they are strongly interacting with each other but at the same time are not easily disturbed by their environment. This has not been possible up to now using technologically relevant materials. Colloidal quantum dots could just be the ticket; they are a proven, commercially appealing solution already employed in the most advanced LCD television displays – and they fulfill all the requirements.

Researchers at Empa and ETH Zurich, led by Maksym Kovalenko, together with colleagues from IBM Research Zurich, have now shown that the most recent generation of quantum dots made of lead halide perovskites offer an elegant and practically convenient path to superfluorescence on-demand. For this, the researchers arranged perovskite quantum dots into a three-dimensional superlattice, which enables the coherent collective emission of photons – thus creating superfluorescence. This provides the basis for sources of entangled multi-photon states, a missing key resource for quantum sensing, quantum imaging and photonic quantum computing.