Quantum computing has advanced significantly in recent years in terms of usability, scalability, and computational capacity. However, since many regions of the world don’t even have access to the existing internet, replacing the world’s internet infrastructure with a whole new system would probably take the better part of a century. Utilizing the present infrastructure for information transmission would be one of the finest approaches for researchers to increase the scalability of the quantum internet.
Now, a research facility in Illinois has shown how to transmit quantum information over large distances using just current fiber optic lines, advancing the idea of a scalable quantum internet. According to Panagiotis Spentzouris, director of Fermilab’s quantum science program, “it is not a small thing to have two national labs, 50 kilometers apart, working on quantum networks with this common spectrum of technical competence and knowledge.”
“To tackle this incredibly difficult and complicated topic, you need a diversified team.” In other words, information-carrying particles are transmitted via a network while both ends of the line are operating in unison. The experiment included moving quantum-encoded photons over a considerable distance while maintaining a high level of synchronization between them.
Here, synchronization is the most challenge. A conventional clock cannot be used to synchronize computers over a network for a variety of security and practical reasons. Even if you purposefully set them to nearly identical timings, if you checked your watch and your friend’s watch, they would still differ by a few hundredths of a second. This just won’t do for traditional computing, hence network time protocol (NTP), which synchronizes all involved computers to within milliseconds of one another, is used for synchronization. Researchers will need to go outside the box to achieve synchrony since quantum computers are considerably pickier and need even fewer margins of error.
While this is no simple task, the researchers put a clock down the same optical fibers they were sending the quantum-encoded photons down, but on a separate wavelength to minimize interference. According to Rajkumar Kettimuthu, an Argonne computer scientist and research team member, “choosing proper wavelengths for the quantum and classical synchronization signals is particularly crucial for reducing interference that may impact the quantum information.”
“One comparison would be to think of wavelengths as lanes on a road and fiber as the road. The clock is a truck, and the photon is a cyclist. The truck may enter the bike lane if we are not careful. So, to ensure that the vehicle kept in its lane, we ran a ton of trials. With only a 5-picosecond discrepancy between the clocks in each site, they were successful. With only existing infrastructure, the researchers were able to send quantum information across a long-distance network with astounding accuracy.
This is the first instance in which genuine optical fiber has been used to demonstrate such high synchronization precision and coexistence with quantum information, according to Spentzouris. This record-breaking performance is a crucial step toward developing real multi-node quantum networks.