The advent of quantum networks presents a unique set of challenges, particularly in maintaining the fragile entangled states necessary for quantum communication. The ability to ensure signal delivery efficiency is crucial for the successful integration of quantum networks into the marketplace. Addressing these challenges, a team of scientists at Qunnect Inc. in Brooklyn, New York, recently achieved a significant milestone by operating a quantum network beneath the streets of New York City. This groundbreaking achievement marks a crucial step forward in quantum communication technology.
Although entangled photons have been transmitted before, the issue of noise and polarization drift in fiber optic environments has posed a significant hurdle in maintaining the coherence of entangled states over extended periods. The team at Qunnect recognized this challenge and set out to develop innovative solutions to overcome these obstacles. Mehdi Namazi, the co-founder and chief science officer at Qunnect, emphasized the importance of their work in addressing these issues and pushing the boundaries of quantum network stability.
Prototype Network Design and Operation
For their prototype network, the researchers at Qunnect utilized a 34-kilometer-long fiber circuit known as the GothamQ loop. Operating with polarization-entangled photons, the team demonstrated an impressive 15-day continuous operation with an uptime of 99.84% and a compensation fidelity of 99% for entangled photon pairs transmitted at a rate of approximately 20,000 per second. Even at higher rates of half a million entangled photon pairs per second, the fidelity remained at a notable 90%. This success signifies a significant advancement in the field of quantum communication.
Polarization plays a crucial role in quantum communication, enabling the creation, manipulation, and measurement of photons. Polarized photons are easy to create and control, making them ideal for quantum applications. Entangled photons, in particular, have been instrumental in developing large-scale quantum repeaters, distributed quantum computing, and quantum sensing networks. The unique properties of entangled photons stem from quantum entanglement, a fundamental phenomenon in quantum physics that has garnered widespread recognition, including the 2022 Nobel Prize in Physics.
One of the key challenges faced by the team at Qunnect was polarization drift, which was found to be both wavelength and time dependent. To address this issue, the researchers designed and implemented active compensation techniques at specific wavelengths. By generating entangled dual-colored photon pairs using rubidium-78 enriched vapor cells, the team successfully mitigated the effects of polarization drift in the fiber environment.
To counteract disturbances in polarization caused by external factors such as vibrations, bending, and fluctuations in pressure and temperature, the Qunnect team developed automated polarization compensation (APC) devices. By utilizing classical photon pairs to measure polarization drift at various distances along the fiber network, the researchers implemented corrective measures to maintain the coherence of entangled photon pairs. This automated approach proved to be effective in ensuring the stability and reliability of the quantum network.
The achievements of the Qunnect team in operating a stable quantum network in a real-world environment are a significant milestone in the field of quantum communication. By addressing the challenges of polarization drift and noise in fiber optic networks, the researchers have demonstrated the feasibility of long-term entangled state transmission. Their work paves the way for the development of practical quantum communication technologies and the realization of a quantum internet. The deployment of rack-mounted equipment, such as Qu-Val, signifies a step towards widespread adoption of quantum communication solutions. With continued research and innovation, the future of quantum networks looks promising, offering unprecedented opportunities for secure and efficient communication technologies.
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