Quantum networks have long been seen as the future of communication and information processing due to their potential for ultra-secure data transfer and quantum computing capabilities. However, one of the major challenges in implementing quantum networks has been the fragility of entangled states in fiber cables and the efficiency of signal delivery. Recently, a team of scientists at Qunnect Inc. in Brooklyn, New York, made a significant breakthrough by successfully operating a quantum network under the streets of New York City.
While previous attempts at transmitting entangled photons have been made, there has been too much noise and polarization drift in the fiber environment for entanglement to survive in the long term. The Qunnect team addressed these challenges by designing a network with active compensation for polarization drift, ensuring the stability of entangled photon pairs over extended periods. Their innovative methods and results were published in PRX Quantum, showcasing their success in overcoming the fragility of entangled states in a fiber cable.
For their prototype network, the researchers at Qunnect used a 34-kilometer-long fiber circuit known as the GothamQ loop. By utilizing polarization-entangled photons, they were able to operate the loop continuously for 15 days with an impressive uptime of 99.84%. The entangled photon pairs were transmitted at a rate of about 20,000 per second, achieving a compensation fidelity of 99%. Even at a higher rate of half a million entangled photon pairs per second, the fidelity remained at nearly 90%. This demonstrates the robustness and efficiency of their network design in maintaining entanglement over long distances.
Polarization-entangled photons have become integral in the development of large-scale quantum repeaters, distributed quantum computing, and distributed quantum sensing networks. These photons are not only easy to create and manipulate but also offer a high level of security for quantum communication. By entangling photons of different wavelengths, such as an infrared photon of 1,324 nanometers and a near-infrared photon of 795 nm, the researchers at Qunnect were able to create a stable and efficient quantum network compatible with existing quantum systems.
One of the key innovations in the Qunnect network is the use of automated polarization compensation (APC) devices to electronically correct for polarization drift in the entangled photon pairs. By sending classical photon pairs of known polarizations down the fiber, they could measure and adjust for any drift caused by external factors such as vibrations, bending, pressure, and temperature fluctuations. This active compensation mechanism ensures the stability and reliability of the entangled photon pairs throughout the network.
The successful demonstration of the GothamQ loop by the Qunnect team represents a significant step forward in the development of practical quantum networks. Their achievement in maintaining entanglement over extended periods, combined with the automation of network operations, brings us closer to a future quantum internet. With the continued advancement of quantum technologies and the implementation of innovative solutions like automated polarization compensation, the dream of a secure and efficient quantum network is becoming a reality.
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