Bichromatic Quantum Teleportation of Weak Coherent Polarization States on a Metropolitan Fiber

TL;DR

This work addresses the practical challenge of performing quantum teleportation over a real-world metropolitan telecom fiber while coexisting with classical network traffic. It combines a bichromatic entangled-photon source (795 nm idler and 1324 nm telecom signal) with a local Bell-state measurement to achieve conditional state transfer of a 795 nm weak coherent input onto a telecom photon and transmits it over a 30 km deployed fiber, followed by polarization-state tomography. The demonstrated fidelities exceed the classical bound (about $F=2/3$) with local teleportation at 92.3% and deployed-fiber teleportation at 90.1% (and ~85.9% under co-propagating C-band traffic), validating the robustness of the approach under carrier-grade conditions. These results, together with the demonstrated coexistence with live data channels, establish a practical device-to-telecom interface for hybrid quantum-classical metro networks and provide a concrete step toward scalable quantum networking in existing infrastructure.

Abstract

As quantum technologies mature, telecommunication operators have a clear opportunity to unlock and scale new services by providing the connectivity layer that links quantum computers, sensors, clocks, and other quantum devices. Realizing this opportunity requires demonstrating quantum networking protocols, including quantum teleportation, under real-world conditions on existing telecom infrastructure. In this work, we demonstrate quantum teleportation over Deutsche Telekom's metropolitan fiber testbed in Berlin using commercial components deployed at the telecom datacenter. A local Bell-state measurement between 795 nm photons from a weak coherent source and from a bichromatic warm-atom entangled photon source enables conditional state transfer onto an O-band photon, which is transmitted through a 30-km field-deployed fiber loop under real-world environmental conditions. The teleported state is reconstructed after propagation via state tomography, achieving an average teleportation fidelity of 90\% on the deployed link. System performance is evaluated in both the absence and the presence of co-propagating C-band classical traffic within the same fiber, demonstrating compatibility with wavelength-division multiplexed telecom infrastructure carrying live data channels.

Figures (6)

• Figure 1: Schematic of the field-deployed teleportation experiment on Deutsche Telekom’s R&D fiber test network in Berlin. A 795-nm weak coherent state (WCS) interferes with the 795-nm idler photon of a bichromatic polarization-entangled pair at a local Bell-state measurement (BSM). Conditional on a successful BSM, the input polarization state is transferred, up to a known unitary, onto the 1324-nm signal photon, which is transmitted over a 30-km deployed fiber and analyzed by polarization tomography. Co-propagating C-band classical traffic is multiplexed onto the same fiber as indicated.
• Figure 2: OTDR trace of the 30-km deployed fiber loop used in this experiment (T-Labs to Dottistraße). Discontinuities correspond to connectors, splices, or patch-panel events. The red line indicates the expected attenuation of standard SMF at 1324 nm (approximately 0.34 dB/km).
• Figure 3: Reconstructed density matrices $\rho$ (real and imaginary parts) from single-state tomography for local teleportation. Matrix elements are shown in the $\{\ket{H},\ket{V}\}$ basis. Positive (negative) values are shown in magenta (blue).
• Figure 4: Density matrices from single-state tomography for the 30-km deployed-fiber configuration without co-propagating classical light. Matrix elements are shown in the $\{\ket{H},\ket{V}\}$ basis. Positive (negative) values are shown in magenta (blue).
• Figure 5: Reconstructed density matrices $\rho$ (real and imaginary parts) from single-state tomography for the 30-km deployed-fiber configuration with co-propagating classical traffic. Matrix elements are shown in the $\{\ket{H},\ket{V}\}$ basis. Positive (negative) values are shown in magenta (blue).