Quantum teleportation using active feed-forward between two Canary Islands (1205.3909v1)

Abstract: Quantum teleportation [1] is a quintessential prerequisite of many quantum information processing protocols [2-4]. By using quantum teleportation, one can circumvent the no-cloning theorem [5] and faithfully transfer unknown quantum states to a party whose location is even unknown over arbitrary distances. Ever since the first experimental demonstrations of quantum teleportation of independent qubits [6] and of squeezed states [7], researchers have progressively extended the communication distance in teleportation, usually without active feed-forward of the classical Bell-state measurement result which is an essential ingredient in future applications such as communication between quantum computers. Here we report the first long-distance quantum teleportation experiment with active feed-forward in real time. The experiment employed two optical links, quantum and classical, over 143 km free space between the two Canary Islands of La Palma and Tenerife. To achieve this, the experiment had to employ novel techniques such as a frequency-uncorrelated polarization-entangled photon pair source, ultra-low-noise single-photon detectors, and entanglement-assisted clock synchronization. The average teleported state fidelity was well beyond the classical limit of 2/3. Furthermore, we confirmed the quality of the quantum teleportation procedure (without feed-forward) by complete quantum process tomography. Our experiment confirms the maturity and applicability of the involved technologies in real-world scenarios, and is a milestone towards future satellite-based quantum teleportation.

• The paper demonstrates a quantum teleportation protocol with active feed-forward that achieves state fidelities significantly above the classical threshold.
• It employs a dual optical channel approach for transmitting entangled photons and Bell-State measurements to perform real-time state corrections.
• The experiment validates advanced techniques like ultra-low-noise detection and entanglement-assisted clock synchronization, paving the way for satellite-based quantum networks.

Quantum Teleportation Using Active Feed-Forward Between Two Canary Islands

The paper under consideration presents a sophisticated quantum teleportation experiment conducted over a 143 km free-space channel between the Canary Islands of La Palma and Tenerife. This paper is notable for its use of active feed-forward operations, which are essential for real-time adaptations in quantum communication protocols, particularly when considering future applications such as satellite-based quantum networks.

Technical Overview

The research team implemented a teleportation protocol by utilizing two optical links—a quantum channel for entangled photon distribution and a classical channel for transmitting the Bell-State Measurement (BSM) results. The key contribution of the paper is the successful demonstration of quantum teleportation with active feed-forward, allowing for the adaptation of the quantum state in real-time based on BSM outcomes.

Key technical elements include:

• Frequency-uncorrelated polarization-entangled photon source: This ensures high-quality entangled photon pairs necessary for the teleportation protocol.
• Ultra-low-noise single-photon detectors: Critical for reducing noise and ensuring high-fidelity teleportation.
• Entanglement-assisted clock synchronization: Provides synchronization between the remote setups on La Palma and Tenerife crucial for aligning detection events.
• Advanced environmental compensation: A closed-loop tracking system managed atmospheric turbulence, a significant challenge for free-space quantum communication.

Experimental Design and Results

The experimental setup involved Alice performing a BSM on La Palma, followed by sending the measurement result via a classical channel to Bob in Tenerife. Bob then used this classical information to apply the correct unitary transformation to his photon, completing the teleportation protocol.

The experiment achieved average teleported state fidelities significantly exceeding the classical limit of 2/3, thereby affirming the quantum nature of the teleportation process. Notably, state fidelities were recorded as 0.890(42), 0.865(46), 0.845(27), and 0.852(37) for various input states.

When implementing the real-time feed-forward operation, the experiment achieved fidelities of 0.760(50) and 0.800(37) for teleported states, further validating the protocol's effectiveness over long distances. The quantum process tomography confirmed the fidelity of teleportation, with a process fidelity of 0.710(42).

Implications and Future Prospects

This work validates crucial technological components for free-space quantum communication, establishing the feasibility of quantum teleportation over significant distances. The experiment supports the potential for deploying quantum networks on a global scale, particularly leveraging satellite-based systems that could bypass terrestrial infrastructure limitations, offering flexible and secure communication channels.

The authors speculate on future applications where teleportation can occur efficiently over lower quality or unknown quantum channels, with the classical channel facilitating high-quality communication or broadcasting capabilities. This research paves the way for advanced quantum networks, where quantum repeaters and long-distance entanglement distribution will be vital for robust quantum information processing across the globe.

In conclusion, this work represents a robust demonstration of quantum teleportation using active feed-forward over extensive free-space distances, marking a significant step toward practical quantum communication systems. Future research may focus on integrating these protocols with existing satellite technologies, as suggested, for enhanced global quantum networking capabilities.