The field of quantum networking has been facing significant challenges in terms of the fragility of entangled states in a fiber cable and ensuring efficient signal delivery. However, recent advancements by scientists at Qunnect Inc. in Brooklyn, New York, have shown promising results in operating a quantum network under the streets of New York City.
The team at Qunnect utilized a leased 34-kilometer-long fiber circuit, named the GothamQ loop, for their prototype quantum network. By employing polarization-entangled photons, they were able to achieve an impressive uptime of 99.84% over a continuous 15-day operation period. The transmission rate of entangled photon pairs reached around 20,000 per second, with a compensation fidelity of 99%. Even at half a million entangled photon pairs per second, the fidelity remained at nearly 90%.
Polarization plays a crucial role in the functioning of quantum networks. The polarization of a photon refers to the direction of its electric field, which can be manipulated and measured easily. Polarization-entangled photons have been instrumental in the development of quantum repeaters, distributed quantum computing, and sensing networks. These entangled photons exhibit a unique quantum phenomenon known as quantum entanglement, which allows particles within a quantum state to have a connection that determines each other’s properties, even over long distances.
One of the key challenges faced in quantum networking is polarization drift, which is both wavelength and time-dependent. To address this issue, Qunnect designed and built equipment for active compensation at specific wavelengths. By generating entangled dual-colored photon pairs using infrared and near-infrared photons, they were able to create a stable quantum network.
Disturbances in polarization due to factors like vibrations, bending, and fluctuations in pressure and temperature can significantly impact the performance of quantum networks. To mitigate these disturbances, the Qunnect team developed automated polarization compensation (APC) devices. These devices electronically corrected the polarization of entangled photon pairs by sending classical photons down the fiber to measure and compensate for any drift.
The successful demonstration of the GothamQ loop by Qunnect represents a significant step towards building a practical entanglement network for a quantum internet. The team’s emphasis on automation, uptime percentage, and operational stability lays the groundwork for future quantum networking technologies. The development of rack-mounted equipment like Qu-Val ensures scalability and adaptability for quantum networks in various environments.
The progress made by Qunnect in operating a quantum network under real-world conditions showcases the potential of quantum networking technologies. By addressing key challenges such as polarization drift and signal delivery efficiency, researchers are paving the way for a future where quantum networks can revolutionize communication and computation. The continued advancements in quantum networking will undoubtedly lead to groundbreaking innovations in the field of quantum information processing.
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