Efficient generation of entangled multiphoton graph states from a single atom

The central technological appeal of quantum science resides in exploiting quantum effects, such as entanglement, for a variety of applications, including computing, communication and sensing(1). The overarching challenge in these fields is to address, control and protect systems of many qubits against decoherence(2). Against this backdrop, optical photons, naturally robust and easy to manipulate, represent ideal qubit carriers. However, the most successful technique so far for creating photonic entanglement(3) is inherently probabilistic and, therefore, subject to severe scalability limitations. Here we report the implementation of a deterministic protocol(4–6) for the creation of photonic entanglement with a single memory atom in a cavity(7). We interleave controlled single-photon emissions with tailored atomic qubit rotations to efficiently grow Greenberger–Horne–Zeilinger (GHZ) states(8) of up to 14 photons and linear cluster states(9) of up to 12 photons with a fidelity lower bounded by 76(6)% and 56(4)%, respectively. Thanks to a source-to-detection efficiency of 43.18(7)% per photon, we measure these large states about once every minute, which is orders of magnitude faster than in any previous experiment(3,10–13). In the future, this rate could be increased even further, the scheme could be extended to two atoms in a cavity(14,15) or several sources could be quantum mechanically coupled(16), to generate higher-dimensional cluster states(17). Overcoming the limitations encountered by probabilistic schemes for photonic entanglement generation, our results may offer a way towards scalable measurement-based quantum computation(18,19) and communication(20,21).