Photonic quantum technologies such as quantum cryptography [1], photonic quantum metrology [2][3][4], photonic quantum simulators and computers [5][6][7] will largely benefit from highly scalable and small footprint quantum photonic circuits. To perform fully on-chip quantum photonic operations, three basic building blocks are required: single-photon sources, photonic circuits and single-photon detectors [8].Highly integrated quantum photonic chips on silicon and related platforms have been demonstrated incorporating only one [9] or two [10] of these basic building blocks.Previous implementations of all three components were mainly limited by laser stray light, making temporal filtering necessary [11] or required complex manipulation to transfer all components onto one chip [12]. So far, a monolithic, simultaneous implementation of all elements demonstrating single-photon operation remains elusive.Here, we present a fully-integrated Hanbury-Brown and Twiss setup on a micron-sized footprint, consisting of a GaAs waveguide embedding quantum dots as single-photon sources, a waveguide beamsplitter and two superconducting nanowire single-photon detectors. This enables a second-order correlation measurement at the single-photon level under both continuous-wave and pulsed resonant excitation.Up to now, most quantum waveguide (WG) circuits have been fabricated from glass-based and Si-based materials. Both material platforms do not allow monolithic integration of deterministic single-photon sources. The used InGaAs/GaAs material system benefits from the capability of directly integrating on-demand non-classical light sources, namely semiconductor quantum dots (QDs) [13]. These emitters reach state-of-the-art performances in terms of single and indistinguishable photon emission, typically via a resonant excitation scheme [14]. Within this platform, single-photon emission in combination with single-mode WGs and beamsplitters (BSs) was demonstrated with and without resonant excitation [15][16][17][18][19][20]. Moreover, the implementation of superconducting nanowire single-photon detectors (SNSPDs) was successfully demonstrated on this material system [11,21,22]. These detectors represent the most suitable choice for working at the single photon level due to their potential near-unity detection efficiency (93 % [23]), low dark count rate and very high time resolution with intrinsic timing jitters in the ps range [24,25].On the other hand, for silicon and silicon-related quantum photonic platforms a high degree of device complexity was reached, but efficient on-demand non-classical light sources are still missing [10]. By using parametric down conversion sources, only probabilistic singlephoton emission is possible and the amount of stray light coming from the intense pump laser prevented so far the implementation of single-photon detectors on the same chip.Electrically-driven sources may solve this issue [12,26], but the used non-resonant excitation scheme typically leads to the emission of photons with a limited degree of i...

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On-chip quantum photonics is a promising route toward the implementation of complex photonic architectures on a small footprint. Therefore, different photonic components demonstrated for off-chip operation must be realized in an integrated manner. An essential building block for the realization of this goal is the integration of efficient on-demand single-photon sources within waveguide circuits. Here, we address this challenge by demonstrating the Purcell-enhanced single-photon emission from an In(Ga)As quantum dot coupled to a high-Q cavity-waveguide device. The combination with a piezoelectric actuator further enables the strain-induced emission energy tuning of the quantum dot as well as the cavity mode. We observe wavelength shifts up to 0.85 nm for the quantum dot, with a differential tuning factor of four between emitter and cavity. This allows for the full compensation of the spectral mismatch between a selected quantum dot and the cavity resonance. A nearly twofold enhancement of the spontaneous emission rate is observed at resonance with the on-demand generation of single photons. This demonstration of a strain-tunable emitter in a waveguide-coupled cavity device represents an essential building block for large scale quantum photonic circuits, especially if combined in the future with miniaturization approaches based on recently developed micromachined piezoelectric actuators.

We extend the analysis of optical transition energies above 1.5 eV in ternary Si x Ge 1−x−y Sn y alloys grown by molecular beam epitaxy to a composition range in which 1−x−y is as low as 0.405. Simple models for transition energies assume a quadratic dependence on material content. Comparing our results to existing predictions of the transition energies based on results obtained from samples with much lower Si and Sn content, however, we find a significant disagreement between experiment and theory, indicating that the assumption of a quadratic dependence might not be valid for the entire composition range of the ternary alloy.

GeSn as a group-IV material opens up new possibilities for realizing photonic device concepts in Si-compatible fabrication processes. Here we present results of the ellipsometric characterization of highly p- and n-type doped Ge_0.95Sn_0.05 alloys deposited on Si substrates investigated in the wavelength range from 1 to 16 μm. We discuss the suitability of these films for integrated plasmonic applications in the infrared region.

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