When shared between remote locations, entanglement opens up fundamentally new capabilities for science and technology [1,2]. Envisioned quantum networks distribute entanglement between their remote matter-based quantum nodes, in which it is stored, processed and used [1]. Pioneering experiments have shown how photons can distribute entanglement between single ions or single atoms a few ten meters apart [3,4] and between two nitrogen-vacancy centres 1 km apart [5]. Here we report on the observation of entanglement between matter (a trapped ion) and light (a photon) over 50 km of optical fibre: a practical distance to start building large-scale quantum networks. Our methods include an efficient source of light-matter entanglement via cavity-QED techniques and a quantum photon converter to the 1550 nm telecom C band. Our methods provide a direct path to entangling remote registers of quantum-logic capable trapped-ion qubits [6][7][8], and the optical atomic clock transitions that they contain [9,10], spaced by hundreds of kilometers.Our network node consists of a 40 Ca + ion in a radiofrequency linear Paul trap with an optical cavity that enhances photon collection on the 854 nm electronic dipole transition. (Figure 1). A Raman laser pulse at 393 nm triggers emission, by the ion, of a photon into the cavity via a bichromatic cavity-mediated Raman transition (CMRT) [11]. Two indistinguishable processes are driven in the CMRT, each leading to the generation of a cavity photon and resulting in entanglement between photon polarisation and the electronic qubit state of the ion of the form 1/ √ 2 (|D J=5/2, mj =−5/2 , V + |D J=5/2, mj =−3/2 , H ), with horizontal (H) and vertical (V ) photon polarisation and two metastable Zeeman states of the ion (D J, mj ) [12]. The total probability of obtaining an on-demand free-space photon out of the ion vacuum chamber (entangled with the ion) is 0.5 ±0.1 [12].While the ∼ 3 dB/km losses suffered by 854 nm photons through state-of-the-art optical fibre allows for few km internode distances, transmission over 50 km would be 10 −15 . 854 nm photons are also frequencyincompatible with other examples of quantum matter, preventing the realisation of ion-hybrid quantum systems over any distance. Single photon frequency conversion to the telecom C band (1550 nm) offers a powerful general solution: this wavelength suffers the minimum fibre transmission losses (∼ 0.18 dB/km) and is therefore an ideal choice for a standard interfacing wavelength for quantum networking. Photons from solid-state memories [14], cold gas memories [15,16], quantum dots and nitrogen-vacancy centres [17] have been converted to telecom wavelengths. Frequency conversion of photons from ions has recently been performed, including to the telecom C band (without entanglement) [18], to the telecom * ben.lanyon@uibk.ac.at, † These authors contributed equally O band with entanglement over 80 m [19] and directly to an atomic Rubidium line at 780 nm [20].We inject single-mode fibre-coupled photons from the ion into a polarisat...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.