Keeping Quantum States in Diamonds: A Small Step Towards Quantum Internet

BEIJING, April 2 (Xinhua) — In a new study, scientists have created a new system that makes it possible to strengthen quantum communication over longer distances. This is a small but crucial step towards quantum Internet.

Keeping Quantum States in Diamonds: A Small Step Towards Quantum Internet

Scanning electron micrographs of devices used to store quantum information to extend the range of quantum communication

We are still in the early stages of a quantum “big development” in which researchers are trying to use strange mathematical systems to control subatomic particles, thereby enhancing computing and communication. For quantum scientists, one of the core goals of the era is to build networks that transmit quantum information on a larger scale, which will advance cryptography, sensing technology and even distributed quantum computing. For now, however, these are theoretical assumptions, and without components such as repeaters to extend the distance of transmission of quantum information, or without sensors that can convert quantum information into photons, such networks cannot really exist. The new study brings the field of quantum communications one step closer to the invention of quantum repeaters.

“Traditional repeaters measure signals and amplify them,” says Mihir Bhaskar, a physics graduate student at Harvard University. When we build quantum networks, we’re trying to do something similar, except that we’re communicating with single-photons. “

Today, our network transmits information in the form of bits, but some natural systems, such as photons or electrons running around atoms, can store richer information through their properties. More importantly, these systems may be entangled, making duplicate measurements at distant points more relevant than conventional probabilities allow. Quantum information scientists believe that in the near future, they may be able to use networks with these attributes to send unbreakable information, improve the functionality of sensors, or perform tasks that we don’t yet imagine.

One of the central challenges in all this is how to solve the difficulty of sending quantum information over long distances. This information is encoded into a single photon, which is likely to be lost in several kilometers of fiber optic cable. Any network that wants to make the distance between the connecting nodes greater than the range of a town requires a repeater to amplify the signal. However, this is a considerable challenge for quantum information networks. Unlike conventional repeaters, it is impossible to replicate a quantum state precisely, because the measurement of the quantum state itself destroys it.

Researchers at Harvard University and the Massachusetts Institute of Technology have developed a central node that effectively reduces the distance information travels in half. The system is set up in a diluted chiller that is near absolute zero and contains a diamond with an “empty seat”. The so-called “empty space” is actually an area created when two carbon atoms are replaced with a single silicon atom, temporarily storing quantum photons at extremely low temperatures inside the diluted chiller.

The system receives incoming photons from point A and then saves the state of the photons (without spoiling them) for long enough to receive a photon from point B. After these photons are synchronized and entangled enough, the central node generates a key that correlates between the two points. At the same time, the key is only meaningful to A and B. The two parties can then use this key to encrypt and decrypt the message.

The researchers published their findings in a recent issue of Nature. Bhaskar explains that this is not a repeater that can transmit quantum information directly from point A to point B, but rather the key missing element that ultimately achieves this goal, which is the intermediate interface between quantum information (stored in the form of light) and intermediate nodes. Researchers are trying to prove that they can send information from point A to a node and then to point B, or even extend the range by placing more diamond units between the two nodes.

Before the system can become part of long-distance quantum communication, researchers will have to make many other improvements. The system needs to work between two truly independent institutions, not just as workstations in the lab. In addition, the system currently works at different wavelengths than the one skewed best suited for fiber optic cables, and requires a way to convert signals into these wavelengths.

Some researchers who were not involved in the study praised the technical achievements of the work. Barry Sanders, director of the Institute of Quantum Science and Technology at the University of Calgary in Canada, said it was “an exciting proof of principle” not only because it showed the way quantum memory is done, but also because measurements confirm edgy between photons. But he also points out that there is still a long way to go before it can be extended to more practical uses.

Prem Kumar, director of the Center for Photon Communication and Computing at Northwestern University, who was also not involved in the study, said it was a noteworthy job and a key step toward the eventual invention of quantum repeaters, even though it was just one of many necessary steps. Kumar also stressed that it is impossible to develop a mature quantum network in a short time.

Scientists around the world are studying various issues in an attempt to develop the ultimate quantum Internet. Researchers have designed fiber optic lines in the Chicago and Boston areas to conduct more similar experiments at shorter distances. Quantum research, led by Pan Jianwei of the University of Science and Technology of China, has succeeded in entangling the preserved quantum state in the laboratory’s 50-kilometer quantum state coil, and using the Moko satellite as an intermediary to entangle photons in different laboratories around the world. However, these are only one part of a larger puzzle that must eventually be integrated and overcome other problems that must be solved. For example, the converter mentioned above must be able to convert quantum information stored in a quantum processor into photons propagated on a fiber.

In any case, the new study is an exciting step forward, but as Kumar says, the quantum Internet of the future is still in the dark, and we’ve just taken the first few steps of the marathon. (Any day)