Long-distance optical quantum channels are necessarily lossy, leading to errors in transmitted quantum information, entanglement degradation, and, ultimately, poor protocol performance. By highlighting the issues around inherent loss that occurs across every form of communication channel, scientists from Griffith University’s Centre for Quantum Dynamics have created a mechanism to reduce that loss.
Scientists performed distillation by ushering amplification to improve a noisy entanglement channel. They subsequently employed entanglement swapping to demonstrate unconditionally improved arbitrary quantum information transmission.
In this way, scientists represented the realization of a genuine quantum relay.
Dr. Sergei Slussarenko from The University of Queensland said, “The study was the first to demonstrate an error reduction method that improved the performance of a channel. First, we looked at the raw data transmitted via our channel and could see a better signal with our method than without it.”
“In our experiment, we first sent a photon through the loss – this photon is not carrying any useful information, so losing it was not a big problem. We could then correct for the effects of loss via a device called noiseless linear amplifier developed at Griffith and the University of Queensland.”
“It can recover the lost quantum state, but it cannot always succeed; sometimes, it fails. However, once the recovery succeeds, we then use a quantum state teleportation protocol to teleport the information we wanted to transmit into the now corrected carrier, avoiding all the loss on the channel.”
“Our work implements a so-called quantum relay, a key ingredient of this long-distance communication network. The no-cloning theorem forbids making copies of unknown quantum data, so if a photon that carries information is lost, the information it carries is gone forever. A working long-distance quantum communication channel needs a mechanism to reduce this information loss, which we did in our experiment.”
“The next step in this study would be to reduce the errors to a level where the team could implement long-distance quantum cryptography and test the method using real-life optical infrastructure, such as those used for fiber-based internet.”
- Slussarenko, S., Weston, M.M., Shalm, L.K. et al. Quantum channel correction outperforming direct transmission. Nat Commun 13, 1832 (2022). DOI: 10.1038/s41467-022-29376-4