The scientists managed to link two quantum memory cells at a distance of more than 50 kilometers, which is almost 40 times the previous record.
This achievement makes the idea of a super-fast, ultra-secure quantum internet much more plausible.
Quantum coupling relies on quantum entanglement, or what Einstein called 'spooky action at a distance': when two particles are inextricably linked and dependent on each other, even if they are not in the same place.
Quantum memory is the quantum equivalent of classical computational memory – the ability to store quantum information and retain it for a long time – and if we're going to get to the stage where quantum computers are truly practical and useful, getting that memory to work is necessary.
“The main implication of this study is to extend the entanglement distance in [optical] fiber between quantum memory to the scale of a city,” said team leader Jian-Wei Pan of the University of Science and Technology of China.
As for the entanglement of photonic (light) particles, we have dealt with this in the past in empty space and on optical fibers at long distances, but adding quantum memory makes the process much more difficult. The researchers speculate that a different type of approach may be better for this: entangling an atom and a photon at successive nodes, where atoms are nodes and photons transmit messages.
With the right network of nodes, you can provide a better foundation for the quantum internet than pure quantum entanglement using only photons.
In this experiment, two blocks of quantum memory were rubidium atoms cooled to a low energy state. When they are associated with entangled photons, each of them becomes part of the system.
Unfortunately, the farther a photon has to travel, the higher the risk of this system being disrupted, which is why this new record is so impressive.
The key is a technique called resonator amplification, which works to reduce photonic coupling losses during entanglement.
Simply put, by placing atoms of quantum memory in special rings, random noise that can interfere and destroy the memory is reduced.
Bound atoms and photons, obtained by amplifying the resonator, form a node. The photons are then converted to a frequency suitable for transmission over telecommunications networks — in this case, a telecommunications network the size of a city.
In this experiment, the nodes of the atoms were located in the same laboratory, but the photons still had to move along cables more than 50 km long. There are problems with actually separating the atoms further, but there is a proof of concept.
“Despite tremendous progress, currently the maximum physical distance reached between two nodes is 1.3 km, and problems with longer distances remain,” the researchers explain in their published article.
“Our experiment could be extended to nodes physically separated by equal distances, which will form a functional segment of the atomic quantum network, paving the way for atomic entanglement at many nodes and at much longer distances.”
Then things will get really interesting. While quantum memory may be the equivalent of computer memory in classical physics, the quantum version should be able to do much more — process information faster and solve problems that go beyond our current computers.
When it comes to transferring this data, quantum technology promises to increase transfer rates and ensure data transfer security, using the very laws of physics – provided we can work reliably over long distances.
“The quantum Internet, connecting remote quantum processors, should enable a number of groundbreaking applications such as distributed quantum computing,” the researchers write. “Its implementation will rely on long-distance communication between distant quantum memories.”
The study was published in the journal Nature.
Sources: Photo: Gerd Altmann / Pixabay
