If a photon interacts with a member of an entangled photon pair via a so-called Bell-state measurement (BSM), its state is teleported over principally arbitrary distances onto the second member of the pair. Starting in 1997, this puzzling prediction of quantum mechanics has been demonstrated many times; however, with one very recent exception, only the photon that received the teleported state, if any, travelled far while the photons partaking in the BSM were always measured closely to where they were created. Here, using the Calgary fibre network, we report quantum teleportation from a telecommunication-wavelength photon, interacting with another telecommunication photon after both have travelled over several kilometres in bee-line, onto a photon at 795~nm wavelength. This improves the distance over which teleportation takes place from 818~m to 6.2~km. Our demonstration establishes an important requirement for quantum repeater-based communications and constitutes a milestone on the path to a global quantum Internet

Photon-based quantum information processing promises new technologies including optical quantum computing, quantum cryptography, and distributed quantum networks. Polarization-encoded photons at telecommunication wavelengths provide a compelling platform for practical realization of these technologies. However, despite important success towards building elementary components compatible with this platform, including sources of entangled photons, efficient single photon detectors, and on-chip quantum circuits, a missing element has been atomic quantum memory that directly allows for reversible mapping of quantum states encoded in the polarization degree of a telecom-wavelength photon. Here we demonstrate the quantum storage and retrieval of polarization states of heralded single-photons at telecom-wavelength by implementing the atomic frequency comb protocol in an ensemble of erbium atoms doped into an optical fiber. Despite remaining limitations in our proof-of-principle demonstration such as small storage efficiency and storage time, our broadband light-matter interface reveals the potential for use in future quantum information processing.Photonic quantum communication technologies rely on encoding quantum information (e.g. qubits) into single photons, and processing and distributing it to distant locations. In principle, a qubit can be encoded into any photonic degree of freedom, but the polarization degree has often been a preferred choice due to the ease of performing single qubit manipulations and projection measurements using wave-plates and polarizing beamsplitters, and the availability of polarization-entangled photon-pair sources [1]. On this background many seminal demonstrations of quantum information processing have employed polarization qubits, such as teleportation [2], entanglement swapping [3], and secure quantum key distribution over more than hundred kilometers [4], pointing towards the possibility to build secure quantum networks [5].In addition to polarization encoding, the realization of future quantum networks will be greatly facilitated by the use of existing fiber optic infrastructure, which allows low propagation loss for photons at wavelengths around 1550 nm, commonly referred to as telecom-wavelengths [6]. Nevertheless, propagation loss still limits the distance of such quantum links to a few hundreds kilometers. This distance barrier may be overcome by the development of quantum repeaters [7]. These, in turn, rely on the ability to store photonic qubits in quantum memories to overcome the probabilistic nature of photon transmission through lossy quantum channels and emission from cur- † J.J. and E.S. contributed equally to this work.rently used single-photon sources [8,9]. However, to date, no quantum memory for polarization qubits encoded into telecom wavelength photons has been demonstrated. In fact, until recently [18], direct quantum storage of telecom-wavelength photons was an unsolved problem. The most promising candidate, erbium, has the required transition wavelength but exhib...

operating at different wavelengths through the exchange of photons. However, so far, only a few investigations have been reported [16-18], and none of them has included a quantum memory functioning at telecommunication wavelength. In this work, we demonstrate entanglement between two atomic frequency comb (AFC)-based quantum memories [19] in ensembles of cryogenically cooled rare-earth ions, one for 794-nmand one for 1535-nm-wavelength photons. The first memory employs a thulium-doped lithium-niobate (Tm 3+ :LiNbO 3) crystal, the second an erbium-doped fiber (Er 3+ :SiO 2). Entanglement is created through the interaction with entangled photons created by spontaneous parametric down-conversion. Both memories allow buffering and re-emitting multiplexed quantum data in feed-forward-controlled spectral or temporal modes, either of which makes them suitable for quantum repeaters [20,21]. It is significant that our experiment involves two classes of ions: Kramers and non-Kramers. Due to their specific electronic configurations, Kramers ions are strongly coupled to the local magnetic environment while non-Kramers ions are relatively immune to magnetic-field fluctuations. These characteristics make Kramers ions strong candidates for quantum sensors while non-Kramers are generally more suitable for quantum memory with long storage time.

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We report quantum teleportation between telecom and 795 nm photons. This improves the distance over which teleportation takes place from 818 m to 6.2 km and constitutes a milestone towards a global quantum internet.

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