Engineers at the California Institute of Technology have shown that atoms in the cavities of optical cavities can become one of the main technologies for the functioning of the quantum Internet. The researchers published their work in the journal Nature.
Quantum networks will connect quantum computers through a special system that will provide a connection between them. In theory, quantum computers will one day be able to perform certain functions faster than classical computing systems, using properties of quantum mechanics, such as superposition of states, which allows quantum bits to be both zero and one at the same time.
As with classical computers, scientists would like to connect multiple quantum computers to exchange data and work together - to create a kind of "quantum internet." This would open the door to a variety of applications, including distributed quantum computing and encrypted communications. However, such a network must be able to transfer information between two devices without changing the quantum properties of the transmitted information.
The current model works like this: One atom or ion acts like a qubit and stores information about its quantum property, such as spin. To read this information and transfer it to another place, the atom must be excited with a pulse of light, causing it to emit a photon whose spin is entangled with the spin of the atom and is equal to it. The photon can then transmit information associated with the atom over a long distance over an optical fiber cable. But doing it is harder than it sounds. Most atoms are sensitive to fluctuations in magnetic and electric fields, which leads to errors in the operation of devices based on them.
To overcome this problem, the Caltech researchers built a nanophotonic resonator - a rod about 10 microns long with a special pattern etched on its surface, made from an yttrium orthovanadate crystal. Then the scientists placed an ion of the rare earth metal ytterbium Yb 3+ in the center. When radiation is transmitted through such a resonator, it passes several times along the rod and, ultimately, having lost enough energy, is absorbed by the ytterbium ion. The authors also showed that cavities in the material change the environment of the ion, so that the emitted photon can stay in the material up to 99% of the time, and scientists, in the meantime, can measure its properties.
In addition, ytterbium ions are able to store information in their back for 30 milliseconds. This is enough to transmit information across the continental United States. The team is currently focused on creating the building blocks of a quantum network. They then hope to expand their experiments and connect the two quantum bits far apart.
Author: Nikita Shevtsev