Quantum teleportation with photons from "artificial atoms"
A novel experimental demonstration of quantum teleportation has been achieved using photons generated on-demand by semiconductor quantum dots, nanostructures that are often referred to as “artificial atoms”. This milestone was the result of the scientific collaboration between the Nanophotonics group of the Physics Department lead by Prof. Rinaldo Trotta, the Institute of Semiconductor and Solid-State Physics of the Johannes Kepler University in Linz (Austria) and the Department of Applied Physics, Royal Institute of Technology, Stockholm (Sweden). The outcome of the research was recently published on the open-access journal Science Advances. The main motivation behind the interest in quantum dots as light sources resides in their capability of emitting either single or entangled photons on-demand—a strict requirement for the efficient implementation of advanced quantum communication protocols. In particular, quantum teleportation is an essential resource to the realization of quantum networks able to distribute qubits over distant nodes. Since quantum communication relies on single particles of light, it is susceptible to losses which cannot be recovered by optical amplifiers due to the no-cloning theorem. The solution is offered by a property with no classical analogue, quantum entanglement. This counterintuitive property, named by Einstein as "spooky action at a distance", is a profound correlation between two particles, such that performing a measurement on one of the entangled partners instantaneously affects the other. If a stream of single photons encoding qubits in their polarization state is combined with a source of entangled photons, it is possible to transfer quantum information from one location to another, with the help of a classical communication channel. The researchers involved in the project identified the optimal choice of materials and nanofabrication process of quantum dots to provide a solid-state entangled photon source with state-of-the-art figures of degree of entanglement and photon indistinguishability. Quantum teleportation was successfully observed using light emitted by an individual quantum dot, independently from the arbitrary polarization qubit transferred in the process. This result strengthens the case for the semiconductor optoelectronic platform as a strong candidate for future quantum networking technologies.