Semiconductor Quantum Dot Photonic Interface

The realisation of quantum computers and quantum transmitters is currently a major field of research. Several basic implementations of such systems have been successfully realised, including photons, atoms, superconducting devices, and quantum dots as media under investigation. Each of these systems has shown advantages. For instance, quantum dots are a formidable system for performing fast quantum gates with comparably long coherence times. On the other hand, photons are unchallenged as carriers of quantum information between distant locations and entangled photon pairs generated by spontaneous parametric down-conversion form a key component of modern quantum communication devices. Thus only the combination of different technologies allows for setting up a complex quantum network. One way to form such a network would be a hybrid system, where quantum dots form registers for qubit calculations while photons could link the distant nodes. As a first step in this direction, quantum interfaces have been demonstrated by strongly coupling the quantum dots to photons in a cavity and demonstrating the generation of indistinguishable single photons. However, by probabilistic interaction of quantum dots to entangled photon pairs generated in spontaneous parametric down-conversion, novel routes towards scalable quantum networks would become accessible. This proposal aims at the realisation of a hybrid quantum system composed of a quantum dot and a Sagnac- interferometer-based source of entangled photon pairs. The probabilistic interaction of the two systems will be experimentally proven by demonstrating photon indistinguishability. The level of indistinguishability will be measured by a Hong-Ou-Mandel-type quantum interference of the photons emitted from the quantum dot and the downconversion source. After successfully demonstrating the compatibility of the two photon sources we plan to teleport the quantum state of the photon emitted from the quantum dot onto the second photon of the entangled photon pair. To our knowledge this would demonstrate the first quantum teleportation between two different quantum systems and it would enable entanglement swapping between two different quantum systems. Furthermore, it is a decisive step towards the realisation of quantum repeaters with semiconductor quantum dots as nodes of the network.