The research group of Prof. Dr. Stephan Reitzenstein from the Technical University of Berlin made progress on single-photon-source photonic integration and published their work in ACS Photonics.

The group of Professor Stephan Reitzenstein at the Technical University of Berlin have recently published significant results in the field of integrated nanophotonics using semiconductor quantum dots (QDs) that are embedded within microcavities. The nanometer-scale QDs act as spectrally pure light emitters similar to atoms, generating single photons on-demand which can be collected and used for advanced quantum technologies such as quantum information processing. The resonator cavities containing the QDs enhance their single-photon emission rate and allow for efficient, directional collection of the photons, as well as offering electrical control of the emission energy (or equivalently, the wavelength) of the photons by applying a voltage across the ends of the cavity. The tuning mechanism relies on a quantum-mechanical effect known as the quantum-confined Stark effect. The novel and exciting part of their work consists in the on-chip integration of an electrically driven microlaser and a tunable single-photon source in a very compact and highly functional device design. With this concept the researchers aim at generating indistinguishable photons be on-chip resonant excitation of the single-photon source. Here, indistinguishability is an essential criterion for applications which rely on quantum interference phenomena, such as linear-optical quantum computation and advanced quantum communication. If the Berlin group succeed in matching the energies of the microlaser and a QD emission energy, this breakthrough device would constitute an ultra-compact resonantly-driven, single-photon source with electrical tuning that can be triggered at the push of a button. The ability to actively tune the single photon energy demonstrated in this paper is a huge step forward in this direction, as it allows for a user to tune the energy of the single photons over a 1.1 meV energy range while the laser energy remains fixed. Further optimizations are under way.

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