Deterministically fabricated spectrally-tunable quantum dot based single-photon source

<p>Deterministically fabricated spectrally-tunable quantum dot based single-photon source<br> Spectrally-tunable quantum light sources are key elements for the realization of long-distance quantum communication. A deterministically fabricated single-photon source with a photon extraction efficiency of &eta;&thinsp;=(20&thinsp;&plusmn;&thinsp;2) %, a maximum tuning range of &Delta;E&thinsp;=&thinsp; 2.5 meV and a minimum g(2)(&tau;&thinsp;=&thinsp;0)&thinsp;=&thinsp;0.03&thinsp;&plusmn;&thinsp;0.02 is presented. The device consists of a single pre-selected quantum dot (QD) monolithically integrated into a microlens that is bonded onto a piezoelectric actuator via gold thermocompression bonding. Here, a thin gold layer simultaneously provides strain transfer and acts as a backside mirror for the QD-microlens to maximize the photon extraction efficiency. The QD-microlens structure is patterned via 3D in-situ electron-beam lithography (EBL), which allows us to pre-select and integrate suitable QDs based on their emission intensity and energy with a spectral accuracy of 1 meV for the final device. Together with strain fine-tuning, this enables the scalable realization of single-photon sources with identical emission energy. Moreover, we show that the emission energy of the source can be stabilized to &micro;eV accuracy by closed-loop optical feedback. Thus, the combination of deterministic fabrication, spectral-tunability and high broadband photon-extraction efficiency makes the QD-microlens single-photon source an interesting building block for the realization of quantum communication networks.</p>