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...

We present an on-chip beamsplitter operating on a single-photon level by means of a quasi-resonantly driven InGaAs/GaAs quantum dot. The single photons are guided by rib waveguides and split into two arms by an evanescent field coupler. Although the waveguides themselves support the fundamental TE and TM modes, the measured degree of polarization (∼90%) reveals the main excitation and propagation of the TE mode. We observe the preserved single-photon nature of a quasi-resonantly excited quantum dot by performing a cross-correlation measurement on the two output arms of the beamsplitter. Additionally, the same quantum dot is investigated under resonant excitation, where the same splitting ratio is observed. An autocorrelation measurement with an off-chip beamsplitter on a single output arm reveal the single-photon nature after evanescent coupling inside the on-chip splitter. Due to their robustness, adjustable splitting ratio, and their easy implementation, rib waveguide beamsplitters with embedded quantum dots provide a promising step towards fully integrated quantum circuits.

The implementation of a fully integrated Hadamard gate on one single chip is currently one of the major goals in the quantum computation and communication community. Prerequisites for such a chip are the integration of single-photon sources and detectors into waveguide structures such as photonic crystals or slab and ridge waveguide. Here, we present an implementation of a single-photon on-chip experiment based on a III-V semiconductor platform.Individual semiconductor quantum dots were used as pulsed single-photon sources integrated in ridge waveguides, and on-chip waveguide-beamsplitter operation is verified on the singlephoton level by performing off-chip photon cross-correlation measurements between the two output ports of the beamsplitter. A careful characterization of the waveguide propagation losses (∼ 0.0068 dB/µm) documents the applicability of such GaAs-based waveguide structures in more complex photonic integrated circuits. The presented work marks an important step towards the realization of fully integrated photonic quantum circuits including on-demand single-photon sources.

We demonstrate resonance fluorescence from single In-GaAs/GaAs quantum dots embedded in a rib waveguide beamsplitter structure operated under pulsed laser excitation. A systematic study on the excitation laser pulse duration depicts that a sufficiently small laser linewidth enables a substantial improved single-photon-to-laser-background ratio inside a waveguide chip. This manifests in the observation of clear Rabi oscillations over two periods of the quantum dot emission as a function of laser excitation power. A photon cross-correlation measurement between the two output arms of an on-chip beamsplitter results in a g(2)(0)=0.18, demonstrating the generation, guiding and splitting of triggered single photons under resonant excitation in an on-chip device. The present results open new perspectives for the implementation of photonic quantum circuits with integrated quantum dots as resonantly-pumped deterministic single-photon sources.