“We have thus laid the foundation for implementing quantum communication systems in the very important microwave range,” says Rudolf Gross, professor of technical physics at the Technical University of Munich and director of the Walther Meißner Institute (WMI), where the experiments took place. “This is a milestone. This puts the quantum internet, based on superconducting circuits and microwave communications, within arm’s reach.”
Years of pioneering work
Researchers at WMI have been pioneering the propagation of quantum microwaves for more than a decade. First, they had to prove that microwave radiation even has quantum mechanical properties. Unlike with visible light, this was extremely challenging from a technical point of view, due to the low energy of the microwave photons.
To eliminate interferences, the experiments were done at temperatures near absolute zero. Using special cooling devices, the physicists ultimately succeeded in demonstrating the principle of entanglement in the microwave range, an important prerequisite for reliable quantum communication.
Wiretapping-proof protocol using entanglement
The physicists’ current work brings them one step closer to the actual application: “Quantum Remote State Preparation,” as they call their communication protocol. A quantum state can be set at a remote location without sending anything directly.
The concept can be visualized as follows: Two people, let’s call them Alice and Bob, are in two different places. While a bit is the smallest piece of information in classical informatics, in quantum communication it is a quantum state.
Source: “The quantum internet is within reach”, Technical University of Munich