Entanglement of Trapped-Ion Qubits Separated by 230 Meters
V. Krutyanskiy, Maria Galli, Vojtech Krcmarsky, Simon Baier, Dario Fioretto, Yunfei Pu, Azadeh Mazloom, Pavel Sekatski, M. Canteri, Markus Teller, Josef Schupp, James Bate, Martin Meraner, Nicolas Sangouard, B. P. Lanyon, Tracy E. Northup
Abstract
We report on an elementary quantum network of two atomic ions separated by 230 m. The ions are trapped in different buildings and connected with 520(2) m of optical fiber. At each network node, the electronic state of an ion is entangled with the polarization state of a single cavity photon; subsequent to interference of the photons at a beam splitter, photon detection heralds entanglement between the two ions. Fidelities of up to (88.0+2.2-4.7)% are achieved with respect to a maximally entangled Bell state, with a success probability of 4×10^{-5}. We analyze the routes to improve these metrics, paving the way for long-distance networks of entangled quantum processors.