A quantum emitter efficiently coupled to a nanophotonic waveguide constitutes a promising system for the realization of single-photon transistors, quantum-logic gates based on giant single-photon nonlinearities, and high bit-rate deterministic single-photon sources. The key figure of merit for such devices is the β-factor, which is the probability for an emitted single photon to be channeled into a desired waveguide mode. We report on the experimental achievement of β = 98.43 ± 0.04% for a quantum dot coupled to a photonic-crystal waveguide, corresponding to a single-emitter cooperativity of η = 62.7 ± 1.5. This constitutes a nearly ideal photon-matter interface where the quantum dot acts effectively as a 1D "artificial" atom, since it interacts almost exclusively with just a single propagating optical mode. The β-factor is found to be remarkably robust to variations in position and emission wavelength of the quantum dots. Our work demonstrates the extraordinary potential of photonic-crystal waveguides for highly efficient single-photon generation and on-chip photon-photon interaction. The proposals of quantum communication [1] and linear-optics quantum computing [2] have been major driving forces for the development of efficient singlephoton (SP) sources [3][4][5]. Furthermore, the access to photon nonlinearities that are sensitive at the SP level [6, 7] would open for novel opportunities of constructing highly efficient deterministic quantum gates [7][8][9][10][11][12][13]. A single quantum emitter that is efficiently coupled to a photonic waveguide [14] would facilitate such a SP nonlinearity, enabling the realization of single-photon switches and diodes [7][8][9], as well as serve as a highly efficient single-photon source. Waveguide-based schemes offer highly efficient and broadband channeling of SPs into a directly usable propagating mode where even the photon detection can be integrated on-chip [15]. The associated SP nonlinearity constitutes a very promising and robust alternative to the technologically demanding schemes based on the anharmonicity of the stronglycoupled emitter-cavity system [16][17][18][19].In the present work we consider a single quantum dot (QD) embedded in a photonic-crystal waveguide (PCW). The important figure of merit is the β-factor:which gives the probability for a single exciton in the QD to recombine by emitting a single photon into the waveguide mode. Γ wg and Γ rad are the rate of decay of the QD into either the guided mode or non-guided radiation modes, whereas Γ nr denotes the intrinsic nonradiative decay rate of the QD. The β-factor is related to the single-emitter cooperativity η = β/(1 − β).[20] Experimentally, the β-factor can be obtained by recording the decay rate of a QD that is coupled to the waveguide Γ c = Γ wg + Γ rad + Γ nr and the rate of an uncoupled QD Γ uc = Γ rad + Γ nr in the case where the difference between the total loss rates (Γ rad + Γ nr ) of the two QDs is negligible. Recent proposals have indicated that the β-factor in PCWs may approach unity ...

A major challenge in quantum optics and quantum information technology is to enhance the interaction between single photons and single quantum emitters.Highly engineered optical cavities are generally implemented requiring nanoscale fabrication precision. We demonstrate a fundamentally different approach in which disorder is used as a resource rather than a nuisance. We generate strongly The interaction between a single photon and a single quantized emitter is the core of cavity quantum electrodynamics (QED) and constitutes a node in a quantum information network (1,2). So far, cavity QED experiments have been realized with a wide range of two-level systems including atoms (3), ions (4), Cooper-pair boxes (5), and semiconductor quantum dots (6-8) coupled to photons confined in a cavity.

We present time-resolved spontaneous emission measurements of single quantum dots embedded in photonic crystal waveguides. Quantum dots that couple to a photonic crystal waveguide are found to decay up to 27 times faster than uncoupled quantum dots. From these measurements beta-factors of up to 0.89 are derived, and an unprecedented large bandwidth of 20 nm is demonstrated. This shows the promising potential of photonic crystal waveguides for efficient single-photon sources. The scaled frequency range over which the enhancement is observed is in excellent agreement with recent theoretical proposals taking into account that the light-matter coupling is strongly enhanced due to the significant slow-down of light in the photonic crystal waveguides.