Single photons coupled to atomic systems have shown to be a promising platform for developing quantum technologies. Yet a bright on-demand, highly pure, and highly indistinguishable single-photon source compatible with atomic platforms is lacking. In this work, we demonstrate such a source based on a strongly interacting Rydberg system. The large optical nonlinearities in a blockaded Rydberg ensemble convert coherent light into a single collective excitation that can be coherently retrieved as a quantum field. We simultaneously observe a fully single-mode (spectral, temporal, spatial, and polarization) efficiency up to 0.098(2), a detector-background-subtracted g ( 2 ) = 5.0 ( 1.6 ) × 10 − 4 , and indistinguishability of 0.980(7), at an average photon production rate of 1.18 ( 2 ) × 10 4 s − 1 . All of these make this system promising for scalable quantum information applications. Furthermore, we investigate the effects of contaminant Rydberg excitations on the source efficiency and observed single-mode efficiencies up to 0.18(2) for lower photon rates. Finally, recognizing that many quantum information protocols require a single photon in a fully single mode, we introduce metrics that take into account all degrees of freedom to benchmark the performance of on-demand sources.

Advances in the distribution of quantum information will likely require entanglement shared across a hybrid quantum network [1][2][3]. Many entanglement protocols require the generation of indistinguishable photons between the various nodes of the network [4,5]. This is challenging in a hybrid environment due to typically large differences in the spectral and temporal characteristics of single photons generated in different systems [1]. Here we show, for the first time, quantum interference between photons generated from a single atomic ion and an atomic ensemble, located in different buildings and linked via optical fibre. Trapped ions are leading candidates for quantum computation and simulation with good matter-to-photon conversion [6][7][8][9][10][11][12][13]. Rydberg excitations in neutral-atom ensembles show great promise as interfaces for the storage and manipulation of photonic qubits with excellent efficiencies [14][15][16][17]. Our measurement of high-visibility interference between photons generated by these two, disparate systems is an important building block for the establishment of a hybrid quantum network.Recently, Rydberg atoms have proven to be a useful tool in the field of quantum information. The strong optical nonlinearity exhibited by neutral-atom Rydberg ensembles enables the construction of single-photon sources [15], gates [16], and transistors [17]. Strong light-matter interactions make them well suited as quantum memories [14], and for implementing quantum repeaters [18,19]. Furthermore, arrays of Rydberg atoms are a powerful new platform for quantum simulation [20, 21]. The continued success of trapped-ion systems in quantum computation [6,7], simulation [8, 9], and communication [12] owes to their long coherence and trapping lifetimes [10], high fidelity operations [11], and ease of generating ion-photon entanglement [12, 13].Given the wide-ranging applications of both platforms, future efforts in quantum information will benefit from the construction of remote hybrid atomic-ensemble-ion networks. Flying photonic qubits provide an excellent means arXiv:1907.04387v1 [quant-ph]