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arXiv:2105.04737 · Physical Review A

Wavelength conversion for single-photon polarization qubits through continuous-variable quantum teleportation

Xi-Wang Luo, Chuanwei Zhang, Irina V. Novikova, Chen Qian, Shengwang Du

Published May 31, 2022• 6 citations
arXivHTMLPDF

Abstract

A quantum internet connects remote quantum processors that need to interact and exchange quantum signals over a long distance through photonic channels. However, these quantum nodes operate at the wavelength ranges unsuitable for long-distance transmission. Therefore, quantum wavelength conversion to telecom bands is crucial for long-distance quantum networks based on optical fiber. Here, we propose wavelength conversion devices for single-photon polarization qubits using continuous-variable quantum teleportation that can efficiently convert qubits between near-infrared (780--795 nm suitable for interacting with atomic quantum nodes) and telecom wavelength (1300--1500 nm suitable for long-distance transmission). The teleportation uses entangled photon fields (i.e., nondegenerate two-mode squeezed state) that can be generated by four-wave mixing in a rubidium atomic gas using a diamond configuration of atomic transitions. The entangled fields can be emitted in two orthogonal polarizations with locked relative phase, making them especially suitable for interfacing with single-photon polarization qubits. Our work may pave the way for the realization of long-distance quantum networks.

DOI
10.1103/physreva.105.052444

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A quantum internet connects remote quantum processors that need to interact and exchange quantum signals over a long distance through photonic channels. However, these quantum nodes operate at the wavelength ranges unsuitable for long-distance transmission. Therefore, quantum wavelength conversion to telecom bands is crucial for long-distance quantum networks based on optical fiber. Here, we propose wavelength conversion devices for single-photon polarization qubits using continuous-variable quantum teleportation that can efficiently convert qubits between near-infrared (780--795 nm suitable for interacting with atomic quantum nodes) and telecom wavelength (1300--1500 nm suitable for long-distance transmission). The teleportation uses entangled photon fields (i.e., nondegenerate two-mode squeezed state) that can be generated by four-wave mixing in a rubidium atomic gas using a diamond configuration of atomic transitions. The entangled fields can be emitted in two orthogonal polarizations with locked relative phase, making them especially suitable for interfacing with single-photon polarization qubits. Our work may pave the way for the realization of long-distance quantum networks.
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A key enabling feature of future quantum networks is interoperability between platforms that operate at different wavelengths and with different qubit encodings. We demonstrate an interface that converts atom-photon entanglement from polarization encoding at an atomic wavelength to time-bin encoding in the telecom C-band. Atom-entangled photons at 854 nm are generated from a single 40^{40}40Ca+^++ ion. After quantum frequency conversion to 1550 nm, the photonic polarization qubit is converted into a time-bin qubit using a fiber-based Mach--Zehnder-like encoder. Full quantum tomography of the final state verifies that the process preserves entanglement with 96.3(4.2)% fidelity. Together with the independent work of Ferrari et al. [arXiv:2607.07805 (2026)], this is the first demonstration of polarization-to-time-bin conversion of photons entangled with a single atomic quantum memory. The telecom-compatible interface enables robust qubit transmission over optical fibers and provides a key building block for heterogeneous quantum networking architectures.
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Quantum teleportation [1] is a cornerstone of quantum information science due to its essential role in several important tasks such as the long-distance transmission of quantum information using quantum repeaters [2–4]. In this context, a challenge of paramount importance is the distribution of entanglement between remote nodes, and to use this entanglement as a resource for long-distance light-to-matter quantum teleportation. We report on the demonstration of quantum teleportation of the polarization state of a telecom-wavelength photon onto the state of a solid-state quantum memory. Entanglement is established between a rare-earth-ion doped crystal storing a single photon that is polarization-entangled with a flying telecom-wavelength photon [5, 6]. The latter is jointly measured, using highly efficient superconducting WSi nanowire single-photon detectors [7], with another flying qubit carrying the polarization state to be teleported, which heralds the teleportation. The fidelity of the polarization state of the photon retrieved from the memory is shown to be greater than the maximum fidelity achievable without entanglement, even when the combined distances travelled by the two flying qubits is 25 km of standard optical fibre. This light-to-matter teleportation channel paves the way towards long-distance implementations of quantum networks with solid-state quantum memories.
Quantum communication aims at generating and distributing entangled pairs of photonic qubits (or flying qubits) at a telecom wavelength between distant sites, in order to implement quantum information protocols, such as quantum key distribution, quantum teleportation and quantum processing. For many quantum protocols, and especially for quantum repeaters, which make quantum communication over long distances much more efficient, storing of entangled states is necessary and represents a crucial step towards the realization of a real quantum network. A current outstanding challenge is thus to implement quantum memories for entangled qubits, carried by telecom photons, that combine high efficiency, long storage time and near-perfect fidelity between the input and output states. With this project, our goal is to merge the techniques of telecom wavelengths qubit distribution with quantum storage at shorter wavelength (typically for atomic transitions). Our idea is to map, via a quantum interface, polarization entangled qubits at a telecom wave- length onto a cold atomic ensemble, serving as a quantum memory device.
Quantum network consisting of separate nodes processing information and linked by quantum channels is a promising and widely investigated general architecture for scalable and distributed quantum computing [1]. The most feasible proposals for realisation of such a network involve matter-based nodes (e.g. trapped atoms or ions or solid-state systems) communicating by photons [2]. This approach combines advantages of long-living and precisely manipulated systems for nodes with fast and convenient for long distance information transfer ones. Implementation of such a scheme opens up a lot of research challenges where establishing a reliable channel for quantum state transfer between two nodes by photons is essential, once the nodes are operating. It would by particularly convenient to have a standard channel that can different systems be talking to and the telecom band photons are good candidates for that because of well-established optical fiber infrastructure. In our work we implement a single photon frequency conversion to telecom band so that quantum systems with different emitting frequencies could be used in such a network. This approach also permits to minimize the losses and increase distances to 10s-kilometre range by exploiting the lowest attenuation band in fibers. The work is aimed in particular on developing device capable of converting photons produced by P3/2-D5/2transition in40Ca+ ion that corresponds to 854.2 nm wavelength as a promising candidate for the network nod.