Abstract
Two-level emitters are the main building blocks of photonic quantum technologies and are model systems for the exploration of quantum optics in the solid state. Most interesting is the strict resonant excitation of such emitters to control their occupation coherently and to generate close to ideal quantum light, which is of utmost importance for applications in photonic quantum technology. To date, the approaches and experiments in this field have been performed exclusively using bulky lasers, which hinders the application of resonantly driven two-level emitters in compact photonic quantum systems. Here we address this issue and present a concept for a compact resonantly driven single-photon source by performing quantum-optical spectroscopy of a two-level system using a compact high-β microlaser as the excitation source. The two-level system is based on a semiconductor quantum dot (QD), which is excited resonantly by a fiber-coupled electrically driven micropillar laser. We dress the excitonic state of the QD under continuous wave excitation, and trigger the emission of single photons with strong multi-photon suppression (, g^{(2)}(0) = 0.02) and high photon indistinguishability (V = 57±9%) via pulsed resonant excitation at 156 MHz. These results clearly demonstrate the high potential of our resonant excitation scheme, which can pave the way for compact electrically driven quantum light sources with excellent quantum properties to enable the implementation of advanced quantum communication protocols.
Highlights
The physics of two-level systems constitutes the basis for quantum optics and quantum cavity electrodynamics
To enable related studies under strict resonant excitation, it is crucial to obtain a microlaser that (a) can be operated electrically under continuous wave (CW) and pulsed operation with an emission pulse width significantly shorter than the spontaneous emission lifetime of the quantum dot (QD), (b) shows single-mode emission with an emission linewidth significantly smaller than the homogeneous linewidth of approximately 1 GHz, (c) is spectrally matched with a target QD within the available temperaturetuning range on the order of 500 GHz, and (d) has sufficiently high optical output power of approximately 100–500 nW at the single-mode fiber output to at least saturate the QD transition
To meet these stringent requirements, we first performed reference measurements using a conventional tunable laser as the excitation source to select a QD showing pronounced and clean resonance fluorescence (RF) at 920 nm, where 920 nm corresponds to the central wavelength reachable by the micropillar lasers within the patterned array
Summary
The physics of two-level systems constitutes the basis for quantum optics and quantum cavity electrodynamics. Single photons are key resources for quantum key distribution using the BB84 protocol and for more advanced schemes, such as the quantum repeater concept for long-distance quantum communication In such protocols and in quantum secure direct communication[6], information is usually encoded in the polarization of the photon, and on-demand sources emitting single photons with high indistinguishability are of major importance for the implementation of these protocols. In this context, semiconductor quantum dots (QDs) are nearly ideal twolevel systems and can act as triggered sources of single photons[7], where specific material properties can even be used for the direct generation of linearly polarized photons[8]. To explore the physics of QDs and the quantum nature of emission, different excitation schemes have been
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