Quantum teleportation across a metropolitan fibre network (1605.08814v1)

Abstract: 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.

• The paper demonstrates quantum state teleportation over 6.2 km using a metropolitan fibre network in Calgary with fidelities exceeding 66% and reaching up to 80%.
• It employs a Bell-state measurement and spontaneous parametric down-conversion to prepare and entangle photons for robust state transfer in real-world conditions.
• The experiment paves the way for scalable quantum repeaters and global quantum communication networks with integrated quantum memories.

Quantum Teleportation Across a Metropolitan Fibre Network

This paper presents an important experimental advancement in quantum communication by demonstrating quantum teleportation using a metropolitan fibre network in Calgary. The research explores the teleportation of quantum states over an extended distance of 6.2 km, from a 1532 nm telecommunications photon to a 795 nm wavelength photon. This achievement surpasses previous teleportation distance records restricted to much less than a kilometer and represents a significant milestone for applications in quantum repeaters and a global quantum internet.

The experimental setup involves three main sites: Alice, Bob, and Charlie. Alice encodes quantum information onto a 1532 nm photon, which is then teleported via entanglement with a second photon traveling in the opposite direction towards Bob. The teleportation process relies on a Bell-state measurement (BSM) at Charlie's location, effectively projecting the quantum information onto Bob's 795 nm photon. The implementation in a real-world fibre network adds complexity and practical significance, addressing real-world challenges such as maintaining photon indistinguishability after transmission through long and noisy fibre channels.

Key technical details and innovations include the use of phase-randomized attenuated laser pulses for quantum state preparation, and the creation and manipulation of photon pairs via spontaneous parametric down-conversion processes. Furthermore, photon arrival time synchronization and polarization maintain coherence between photons, mitigating temporal and polarization drifts due to environmental variations. Active feedback systems are demonstrated to be essential to achieving successful teleportation in the deployed setup.

A significant finding from this paper is the confirmation of quantum state transfer with fidelities exceeding 66%, the threshold for classical teleportation, with individual state fidelities reaching up to 80%. The fidelity data was assessed utilizing a decoy-state method, which provides robustness against potential deviations caused by multi-photon emissions from the sources or other noise factors intrinsic to weak coherent pulse systems.

The theoretical and practical implications of these results are profound. Achieving successful long-distance quantum teleportation with the mid-point configuration suggests a feasible path towards scalable quantum networks using quantum repeaters. By enabling the teleportation of entanglement over these distances, it allows for the construction of extended quantum communication links, ideal for distributed quantum computing and secure communication protocols.

Looking forward, the work points towards increased distances and improved efficiencies in real-world quantum communication networks. The methodology and findings pave the way for further research focused on integrating quantum memories and exploring more extensive quantum networking architectures, essential steps toward the realization of a quantum internet. As quantum technologies develop, efforts building upon this experimental framework are expected to incorporate more advanced materials and methods for enhanced performance and scalability in quantum information applications.