“Vienna physicists had set up a fiber optic network for the first time in 2018, through which several participants were able to communicate with each other in an interception-proof manner thanks to quantum cryptography encryption. For the time being, this only worked with four people and rather small data rates, but in principle this was the birth of quantum Internet – a visionary Internet in which data theft and manipulation will be excluded.
In today’s Internet, various encryption methods ensure that sensitive data is transmitted securely. Whenever the browser displays a web page with “https”, it means that data is exchanged encrypted with this Internet connection.
However, today’s methods of data encryption may not be sufficiently secure in the foreseeable future, namely when so-called quantum computers are available to crack today’s coding.
There are repeated reports of progress in the development of quantum computers, but the first prototypes of such systems are not yet a threat to the encryption used today on the Internet.
But if one day the quantum information scientists can build sufficiently powerful codebreakers, then in need the saving will also arise. Quantum technology will then also be able to enable eavesdropping-proof quantum networks through which quantum computers can communicate securely via quantum internet.
In principle, this is already possible today, as the Vienna Pioneer Network has shown. In 2017, China even launched a quantum satellite that can exchange quantum-cryptographically encrypted data with a ground station.
The problem with this technique, however, is the still very low data rate. It is simply not sufficient for many applications today. The high technical use of quantum cryptography is therefore only worthwhile for small amounts of data, which are however important and very secret.
Quantum cryptography as well as quantum computers are used with so-called quantum bits (abbreviated qubits). The physical carrier of a qubit is a particle of matter or light that can be in two different states.
Classical digital technology also operates with two states, zero and one. However, in addition to zero and one, the qubit can also accept these two states at the same time.
Eavesdropping-proof transmission of qubits is also known as teleportation. This term still evokes the memory of the “beaming” in “Spaceship Enterprise” for many people. But when the researchers from the Vienna Institute for Quantum Optics and Quantum Information teleport data in an interception-proof manner, no matter is reported from A to B.
Rather, intertwined photons, i.e. light particles, are sent on the journey. It means that two photons know each other and their states over long distances. In practice, this means that the interception of a photon sent from the sender to the recipient would definitely be noticed.
The Viennese researchers, whose institute belongs to the Austrian Academy of Sciences, are now reporting in the journal “Physical Review Letters” about the next important step towards quantum internet.
Together with quantum physicists from the University of Science and Technology of China, they have succeeded in transmitting three-dimensional quantum states for the first time internationally. The researchers did not work with qubits, but for the first time with so-called qutrits – i.e. three-level states. Certain properties of the quantum system can therefore assume not only two states (0 and 1), but three states (0, 1 and 2).
As early as the 1990s, theoretical work had shown that three-dimensional quantum teleportation should also be possible. “However, we had to develop the actual realization in the laboratory and the technology required for this,” says Manuael Erhard of the Vienna Institute for Quantum Optics and Quantum Information.
What is interesting for the practical application is that more information can be transmitted simultaneously with Qutrits than with qubits. The step of two to three may not sound revolutionary, but this type of data transfer is not limited to three dimensions.
Pri This can be extended to any number of dimensions, Erhard emphasizes. And then the quantum Internet with a sufficient transmission quality moves a lot closer to the realm of the possible.
“The foundation for the next generation of quantum cryptography systems is laid by our basic research today,” commented Jian-Wie Pan, a scientist involved in the project at the University of Science and Technolgoy of China.
The technology of three- or higher-dimensional quantum states is not only of interest for eavesdropping-proof teleportation. Working with higher-dimensional quantum states could also play a central role in the development of practical quantum computers.
This article was first published in August 2019.