Ronald Hanson

We present a deployed quantum link between the Dutch cities Delft and The Hague separated by 10 kilometers, capable of generating solid-state heralded entanglement. This link is realized by employing NV center end nodes, connecting them with state-of-the-art Quantum Frequency Converters and a phase-stabilized architecture over 25 kilometers of telecom fiber. By capitalizing on the full heralding capabilities of the network link in combination with real-time feedback logic on the long-lived qubits, we demonstrate the delivery of a predefined entangled state on the nodes irrespective of the detector outcome. The extendable design, real-time control and compatibility with other qubit platforms and makes this architecture an excellent candidate for future metropolitan scale quantum networks.

Entanglement – the property that particles can share a single quantum state – is arguably the most counterintuitive yet potentially most powerful element in quantum theory. The non-local features of quantum theory are highlighted by the conflict between entanglement and local causality discovered by John Bell. Decades of Bell inequality tests, culminating in a series of loophole-free tests in 2015, have confirmed the non- locality of nature [1]. Future quantum networks [2] may harness these unique features of entanglement in a range of exciting applications, such as quantum computation and simulation, secure communication, enhanced metrology for astronomy and time-keeping as well as fundamental investigations. To fulfill these promises, a strong worldwide effort is ongoing to gain precise control over the full quantum dynamics of multi-particle nodes and to wire them up using quantum-photonic channels. Here I will present recent and ongoing work with the specific target of realizing the first multi-node network wired by quantum entanglement, including first primitive network experiments [3,4] using diamond-based quantum network nodes. [1] For a popular account of these experiments, see e.g. Ronald Hanson and Krister Shalm, Scientific American 319, 58-65 (2018). [2] Quantum internet: A vision for the road ahead, S Wehner, D Elkouss, R Hanson, Science 362 (6412), eaam9288 (2018). [3] N. Kalb et al., Science 356, 928 (2017). [4] P.C. Humphreys et al., Nature 558, 268 (2018).