The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot's excited state. We obtain a lower bound on the fidelity of entanglement of 0.59 ± 0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement based spin-spin entanglement which does not require subnanosecond timing resolution, we estimate that this system would enable near ideal performance.The inferred (usable) entanglement generation rate is 3 × 10 3 s −1 . This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network. 1A single electron spin confined to a charged semiconductor quantum dot (QD) can effectively serve as a single quantum storage device with fast information processing for quantum computing architectures [1][2][3]. QD architectures are excellent candidates for scalable quantum information applications since they are compatible with existing semiconductor processing infrastructure. In addition, site-controlled QD growth has been demonstrated [4,5], and single QDs have been integrated with photonic crystal cavities [6,7], offering significant advantages of optically driven QD spins over other modern quantum information systems. In order to construct a scalable architecture, quantum information must be coherently transferrable between electron spin qubits in separate nodes. The photons emitted from an excited, negatively charged QD (called a trion: a multi-particle state comprised of two electrons and one hole) provide an attractive messenger to carry this information.Recently, optical initialization, rotation and readout of a single electron spin qubit in a single QD were accomplished, demonstrating the QD spin's usefulness as a single qubit [8][9][10][11].Scaling the architecture to arbitrary size requires the ability to entangle the spin qubits of spatially distinct QDs, recently demonstrated by using the tunneling interaction between spatially adjacent QDs [12]. One scaling approach that does not require local interactions instead uses photon qubits to entangle the QDs [13][14][15][16]. If the photons emitted from two QDs are indistinguishable, coincidence measurements can be performed on the emitted photons to probabilistically entangle the source QDs [13,14,17,18]. The first step in protocols of this nature is establishing the entanglement between a single emitted photon an...

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SignificanceTraditional atom–light coupling techniques have propelled the field of quantum optics and atomic physics. Now, by drawing on spectacular improvements in nanofabrication and nanophotonics, we advance a different platform for studying atom–light interactions. The data and simulations presented here are a first step in understanding how cold atoms are delivered to these nanophotonic structures.

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Neutral atom qubits with Rydberg-mediated interactions are a leading platform for developing large-scale coherent quantum systems. In the majority of experiments to date, the Rydberg states are not trapped by the same potential that confines ground state atoms, resulting in atom loss and constraints on the achievable interaction time. In this work, we demonstrate that the Rydberg states of an alkaline earth atom, ytterbium, can be stably trapped by the same red-detuned optical tweezer that also confines the ground state, by leveraging the polarizability of the Yb + ion core. Using the previously unobserved 3 S1 series, we demonstrate trapped Rydberg atom lifetimes exceeding 100 µs, and observe no evidence of auto-or photo-ionization from the trap light for these states. We measure a coherence time of T2 = 59 µs between two Rydberg levels, exceeding the 28 µs lifetime of untrapped Rydberg atoms under the same conditions. These results are promising for extending the interaction time of Rydberg atom arrays for quantum simulation and computing, and are vital to capitalize on the extended Rydberg lifetimes in circular states or cryogenic environments.