By Casimer DeCusatis
One of the most highly anticipated sessions at this year’s OFC conference was the symposium on quantum information science and technology in the context of optical communications. While quantum information science covers a broad range of topics including quantum sensors and computer algorithms, some of the most interesting presentations are from leading telecom providers worldwide related to the development of quantum communication systems. Photonics plays a major role in these systems, and holds great potential for next generation voice and data networks. This month, we’ll look at some of the exciting recent developments in this field.
Quantum Technology Has Become Big Business
Quantum technology has become big business, and many companies are leveraging their relationships with start-ups or academic partners to gain a first-mover advantage in this market. For example, Honeywell Quantum Solutions recently announced its upcoming merger with Cambridge Quantum Computing, to be completed in the third quarter of 2021. Honeywell plans to invest about $300 Million in the as-yet-unnamed new company, whose stated goals include developing both hardware and software full stack integration of their respective solutions. While deals like this are impressive, they further underscore the emerging need for interconnecting quantum computers over extended distances using advanced fiber optic technology.
As discussed during the OFC symposium, conventional fiber optic networks cannot be used to transmit quantum states over the Internet. Small changes in temperature or other ambient conditions cause fibers to expand or contract slightly, which is enough to destroy the fragile quantum coherence state of a qubit. Currently, qubits are encoded as a phase delay in a weak optical pulse, and it’s not practical to preserve this phase delay with sufficient accuracy over long spans of fiber. Transmission of quantum states is useful in many practical problems. Once of the most mature applications is quantum key distribution, which currently requires a separate, dedicated fiber network and operates over limited distances.
British Telecom and Toshiba
Last year, British Telecom in collaboration with Toshiba, demonstrated the first quantum-safe fiber optic network in the United Kingdom). Funded by the AQuaSec Project, a quantum communication research initiative valued at nearly 6 billion pounds, this project was the first of its kind to multiplex data and quantum keys on the same fiber, eliminating the need for a separate redundant network just for key distribution. The initial deployment covered 6 km, but was scalable to around 120 km using standard Openreach fiber. This system transmits thousands of quantum keys per second, replacing a manual key distribution process between several leading research organizations in the United Kingdom. With some variations, this approach can be scaled up to around 200 km or so, but until recently this was the maximum achievable distance for this type of quantum optical communication network.
Within the past year, Toshiba has set a new record for quantum key distribution in optical fiber (600 km) using a technique called dual band stabilization. To minimize phase fluctuations, two optical signals are transmitted at different wavelengths in the same fiber. The first wavelength is used to cancel out phase fluctuations, while the second wavelength transmits optical qubits and provides fine adjustments of the signal phase. Even after propagation through hundreds of kilometers of fiber, this approach can stabilize optical phase to within tens of nanometers, or a fraction of a wavelength. Details on Toshiba’s twin-field quantum key distribution system were recently published in the journal, Nature. This solution also benefits from Toshiba’s previously announced Active Stabilization technology, which automatically adjusts for temperature-induced changes in fiber length without the need for manual recalibration of the network.
Quantum Topics at OFC
These techniques were discussed by British Telecom at the OFC symposium this past year, which also included presentations from industry leaders such as Telefonica in Spain, CNRS in France, and various organizations in China. This symposium concentrated on the service provider and network operator perspectives and deployment experiences of quantum key distribution, and how this technology can be integrated into a full scale production environment. Photonic quantum communications and computing are still evolving technologies, as evidenced by the significant improvements in quantum key distribution demonstrated during the past year alone. It’s exciting to speculate on what this field might accomplish in the coming year, and we can expect to see more innovation in this field when OFC returns to San Diego in March 2022. You still have until 19 October to submit your own paper and until 16 November to submit something for the Demo Zone.
What do you think are the biggest hurdles for a quantum internet? Drop me a line on Twitter (@Dr_Casimer) and maybe we’ll discuss your ideas in a future blog. For cited sources, please contact @Dr_Casimer on Twitter.
Submit Your Paper to OFC by 19 October 2021
Posted: 2 September 2021 by
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