Chinese researchers smash the record for realising two entangled quantum memories at maximum distance

Quantum entanglement can be used to create encrypted communications channels that are secured against hacking

A Chinese research team claims to have smashed the previous record for maintaining two quantum memories in an entangled state at maximum distance.

According to the researchers, they were able to realise entanglement of two quantum memories over 22 kilometres of field-deployed fibres via two-photon interference. With this feat, they smashed the 1.3-kilometre record achieved during previous quantum memory experiments.

The researchers said that they were also able to achieve entanglement over 50 kilometres of coiled fibres via single-photon interference.

The researchers used two quantum memories that were each made of about 100 million extremely cold rubidium atoms

Quantum entanglement is a phenomenon in which two particles become indistinguishably linked, and whatever happens to one particle instantly affects the other, irrespective of the distance between them.

According to the researchers, entanglement can be used to create encrypted communications channels that are secured against hacking by the laws of quantum physics.

Researchers earlier realised entanglement of individual photons across distances beyond 1,000 kilometres. But, entanglement becomes much harder to achieve for larger systems of particles.

In the current study, the researchers used two quantum memories that were each made of about 100 million extremely cold rubidium atoms.

The team entangled the quantum state of each system with the state of a single photon and then sent both photons through the fibre-optic cables

They encoded information onto the clouds of atoms and then extracted a photon from each cloud. The team entangled the quantum state of each system with the state of a single photon and then sent both photons through the fibre-optic cables.

When Bell measurement was performed simultaneously on two photons, the quantum memories with which the photons were paired became entangled to one another.

In this experiment, the entanglement of two quantum memories was maintained over 22 kilometres of fibre-optic cable, installed underground.

In another experiment, the team managed to entangle quantum memories across 50 kilometres using cables that were coiled up in the lab.

"Our experiment could be extended to nodes physically separated by similar distances, which would thus form a functional segment of the atomic quantum network, paving the way towards establishing atomic entanglement over many nodes and over much longer distances," the researchers said.

The study was jointly conducted by researchers from the University of Science and Technology of China (USTC), Shanghai Institute of Microsystem and Information Technology, and Jinan Institute of Quantum Technology.

The detailed findings of the study are published in journal Nature.