A group of scientists from the QuTech research institute in the Netherlands has taken a step that will bring the moment when real quantum computer networks emerge much closer. This step was the technology of quantum teleportation of information between two network nodes that are not directly connected to each other.
As their name implies, quantum computers use some of the bizarre principles of quantum mechanics to perform calculations at speeds that are far beyond the reach of traditional computers. And just as traditional computers are networked using the Internet, quantum computers will need to be networked to be able to realise their full potential. However, sharing quantum information is more complicated than sharing conventional information, because quantum information, by its very nature, is highly sensitive to outside interference, which could lead to its complete loss.
However, quantum information can be teleported from one point to another, thanks to a phenomenon called quantum entanglement, rather than being transmitted in the usual way. Under certain conditions, two particles can get a two-way communication and any change of state of one of the particles will instantly manifest in the second entangled particle, even if they are separated by a distance, which in theory could be as large as desired. This phenomenon, which Albert Einstein called "ghost action at a distance" has been repeatedly verified experimentally and it is used in almost all existing quantum technologies.
In the context of a quantum computer network, quantum bits (qubits) - the carriers of quantum information - can be teleported from one network node to another by affecting one of the entangled pair particles. This technology of quantum information transfer works when there is a direct entanglement quantum entanglement link between two nodes in a network. But computer networks usually have a very complex branched structure, and it is not always possible to establish a direct link between any two nodes.
Typically, a network requires at least one or more intermediate nodes through which the information being transmitted passes. In this case, the QuTech researchers used three vacancy-based qubits in a diamond crystal, which can be provisionally named Alice, Bob and Charlie. To create a primitive network, the researchers created entanglement between Alice and Bob, Bob and Charlie. And as a result, Alice and Charlie also became entangled, using Bob as an intermediary.
To teleport information from Charlie to Alice, Charlie's cubit is set to the appropriate state, 1, 0 or quantum superposition state, 1 and 0 simultaneously. The information transfer process involves a Bell-state measurement (BSM) procedure, which initiates the teleportation of information through an intermediate node and the result of which gives Ellis the key to decrypt the information received.
Repeating the procedure of data teleportation several times, the QuTech scientists have assessed the level of error, the accuracy of information transfer was 71 percent on average. Such a high rate was achieved by using several different methods to ensure the preservation of quantum information, while reducing the intrinsic noise in the quantum system.
As a result of all this, QuTech scientists have created what can be considered the fundamental standard building block of a quantum communication network. In the future, scientists plan to increase the number of qubits in this system in order to expand the network's functionality. In parallel, they will develop methods that will enable data already stored in quantum memory to be transmitted across the network, rather than the message data already being generated by the quantum network.