Physicists entangle quantum memories across a record-breaking 420 km
Optical fibers are already the backbone of global communication systems. Recently, however, physicists have started to explore how their functionality could be boosted further by conveying information via entangled quantum particles—potentially enabling instantaneous exchanges of information across vast distances. Such a system could eventually be the basis of a future 'quantum internet,'…
Physicists have entangled quantum memories over a record-breaking 420 kilometers of optical fiber, pushing the boundaries of what was previously thought possible. This achievement, published in Physical Review Letters by a team led by Xi-Yu Luo at the University of Science and Technology of China, could pave the way for a quantum internet with unparalleled security and computing power.
Traditionally, entangled photons could maintain their quantum information over distances up to 404 kilometers, but surpassing this limit has been a significant challenge due to photon absorption in optical fibers and the exponential decline in photon survival rates. To overcome these hurdles, Luo's team employed the Duan-Lukin-Cirac-Zoller (DLCZ) scheme, a method that utilizes clouds of ultracold atoms cooled to near absolute zero temperatures at each end of the fiber.
These atom clouds emit single photons carrying a portion of their quantum state, which then travel the long distance and are compared at a meeting point to confirm entanglement.
The team converted the atoms' photons to telecommunications wavelengths, which experience significantly less loss in optical fibers. They also implemented a stabilization system to minimize the effects of vibrations and temperature fluctuations that could disrupt the delicate timing required for photon interference. These innovations allowed the researchers to successfully entangle two atom clouds separated by 420 kilometers, a distance that surpassed the previous theoretical limit for direct entanglement transmission.
This breakthrough demonstrates that memory-based quantum networks can outperform direct transmission methods over long distances, promising a future of robust, long-distance connections between quantum computers and ultimately, secure global communication networks.
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