Linking Two Quantum Dots with Single Photons

In the future, encrypting messages and solving hard computational tasks may come to rely on a quantum internet, in which stationary quantum nodes share information via “flying” qubits [1]. The fixed components might be some sort of atomic or solid-state system that encodes information in electronic or spin states, while the flying elements will almost certainly be photons, as only light is capable of long-distance transport of quantum states without loss from decoherence. Transferring quantum information between these different media is a major challenge requiring a number of steps: encoding quantum states from an initial qubit onto photons, low-loss transmission of those photons, and then coherent absorption of those photons by a second qubit. A group led by Atac Imamoğlu at the Swiss Federal Institute of Technology (ETH) in Zurich, Switzerland, succeeded in realizing all these steps with two semiconductor quantum dots separated by 5 m [2]. The experiment is unique in that the two dots are linked together by a single photon qubit, and the successful state transfer is indicated by a scattered photon from the second dot.