QUROPE Quantum Information Processing and Communication in Europe

Single-photon emitters have been considered for applications in quantum information processing, quantum cryptography and metrology. For the sake of integration and to provide an electron photon interface, it is of great interest to stimulate single-photon emission by electrical excitation as demonstrated for quantum dots. Because of low exciton binding energies, it has so far not been possible to detect sub-Poissonian photon statistics of electrically driven quantum dots at room temperature.

The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV− into the neutral state NV0 under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode.

Single-photon sources that provide non-classical light states on demand have a broad range of applications in quantum communication, quantum computing and metrology. Single-photon emission has been demonstrated using single atoms, ions, molecules, diamond colour centres and semiconductor quantum dots.

Optical studies of individual molecules offer the unique possibility of investigating the local environment of single quantum objects on nanometre length scales and of employing molecular systems as non-classical light sources at room temperature. Usually, single molecule excitation is based on optical stimulation by laser radiation. In this feature article, we present an alternative approach by utilizing charge injection in combination with molecular electron–hole recombination to electrically excite single fluorescent dyes.

Single molecule studies are limited to a defined class of organic dye molecules inserted into respective host materials. Basic requirements for suited material combinations include high photon emission rates and long term photostability. A majority of known aromatic host–guest systems employ crystalline organic matrices to prevent dye molecules from uncontrolled reactions with contaminants. However, in terms of device fabrication and technological potentials it is often desirable to use polymers as room temperature host matrices.

Plasmonic nanoantennas can enhance the radiative decay rate of quantum emitters via the Purcell-effect. Similar to their radiofrequency equivalents, they can also direct the emitted light into preferential directions. In this paper we first investigate plasmonic Yagi-Uda antennas that are able to confine light to and direct light from subwavelength size volumes. Hence, enhanced transition rates and directed emission are expected when near-field coupling between quantum emitters and the antennas is achieved.

Plasmonic nanoantennas can enhance the radiative decay rate of quantum emitters via the Purcell-effect. Similar to their radiofrequency equivalents, they can also direct the emitted light into preferential directions. In this paper we first investigate plasmonic Yagi-Uda antennas that are able to confine light to and direct light from subwavelength size volumes. Hence, enhanced transition rates and directed emission are expected when near-field coupling between quantum emitters and the antennas is achieved.