Establishing the ultimate limits of quantum communication networks

At the moment, the data is typically encrypted and then sent across the world to the digital world. However, the data can be vulnerable to hackers.

Quantum communication takes advantage of the laws of quantum physics to protect data. These laws allow particles-typically photons of light-to-transmitted data using quantum bits, or qubits.

Superior capabilities

Multinational corporations, such as IBM and Google, are now building intermediate-size quantum computers with increasing numbers of quantum units or qubits.

Once they have been scaled up to larger sizes, these devices will have greater capabilities than current classical computers. For instance, they can process extremely large numbers in just a few seconds, and even perfectly simulate molecular and biological processes.

One challenge will be connected quantum computers together, in order to create a quantum-version of the Internet or "quantum Internet."

However, an important goal remains unanswered question: what is the ultimate rate of which one can transmit secret messages or quantum systems from one remote quantum computer to another?

Notoriously difficult

Writing in the newspaper Communications Physics, Professor Stefano Pirandola, from the University of York's Department of Computer Science, said scientists have answered the question.

Prof Pirandola studied the optimal working mechanism of a future quantum Internet, and also provided the ultimate secret-key capabilities that can be achieved.

He said: "Studying quantum networks is notoriously difficult, but recent mathematical tools have been developed in quantum networks.

qubits

An outstanding question was to compute the maximum number of elementary quantum systems (known as qubits) that could be reliably transmitted from one network to another, or similarly, to the maximum number of completely secret bits that these remote users could share.

"This number has now a precise analytical formula."

Moreover, the study reveals that the classical-inspired strategy of simultaneous transmission of multiple routes of the network can remarkably boost the rate, i.e., the speed of the quantum communication between any two remote users.