Twenty-five years ago, a group of theoretical physicists from the University of Innsbruck put forth a groundbreaking proposal: a method for transmitting quantum information across vast distances using quantum repeaters. This pioneering concept held the promise of establishing a global network for quantum information exchange.
Fast forward to the present day, and a new generation of researchers from Innsbruck has successfully constructed a quantum repeater node tailored for telecommunication networks’ standard wavelength. In a significant achievement, they have managed to transmit quantum information over tens of kilometers, marking a major milestone in the field. Their remarkable accomplishment has been documented in the esteemed journal Physical Review Letters.
Quantum networks serve as the backbone for connecting quantum processors and quantum sensors, enabling secure communication and facilitating the development of highly efficient distributed sensor networks. These networks rely on the exchange of quantum information via photons traveling through optical waveguides. However, when covering long distances, the chances of photon loss increase significantly, posing a significant challenge.
Unlike classical information, quantum information cannot be easily copied or amplified. Recognizing this constraint a quarter century ago, a group comprising Hans Briegel, Wolfgang Dür, Ignacio Cirac, and Peter Zoller, all associated with the University of Innsbruck at the time, devised the foundational principles for a quantum repeater. Their visionary blueprint incorporated entanglement sources and memories based on the interaction of light and matter. These components enabled the creation of entanglement within independent network links, which could then be interconnected through a process known as entanglement swapping. This ingenious scheme ultimately allowed for the distribution of entanglement across extensive distances.
Even transmission over 800 kilometers possible
Led by Ben Lanyon, a team of quantum physicists from the Department of Experimental Physics at the University of Innsbruck has achieved a significant breakthrough by constructing the fundamental components of a quantum repeater. This remarkable feat involved the creation of a fully operational network node, comprising two individual matter systems capable of generating entanglement with a photon at the standard frequency used in telecommunications networks, as well as conducting entanglement swapping operations.
The quantum repeater node developed by the researchers encompasses two calcium ions that are confined within an ion trap situated within an optical resonator. Additionally, the system enables the conversion of single photons to the telecom wavelength, further enhancing its functionality. To demonstrate its capabilities, the scientists successfully transferred quantum information over a 50-kilometer-long optical fiber. Remarkably, the quantum repeater was positioned precisely at the midpoint between the starting and ending points of the transmission.
Moreover, the team conducted calculations to determine the necessary enhancements required to enable transmission over a distance of 800 kilometers. Such advancements would facilitate the connection between Innsbruck and Vienna, paving the way for an extended quantum information network spanning significant geographical regions.
Source: University of Innsbruck