Scientists reached a record for the transfer of quantum entanglement over a range of fifty kilometers

Image Credits: IQOQI Innsbruck/Harald Ritsch

The idea behind quantum internet is the transmission of information in the form of quantum bits (qubits) between 2 separated quantum processors. Overall, quantum entanglement is pretty well suited for tasks that require coordination, synchronization, or privacy. Secure communications are seen as one of the holy grails that potentially could be achieved with quantum internet. It is therefore not a big surprise that the U.S. Army is interested in this technology.

Scientists at the University of Innsbruck funded by the U.S. Army achieved a record for the transfer of quantum entanglement between matter and light over a distance of 50 kilometers (approximately 31 miles). They shared their findings in the journal: Nature Quantum Information (npj)

Entanglement is a correlation that can be generated between quantum objects such as qubits. When two qubits are entangled, and an observation is made on one, it will affect the outcome of a measurement made on the other, even if that second qubit is materially far away from the first qubit.

Dr. Ben Lanyon, the principal investigator for the project, stated that the achieved record distance of 50 kilometers is 2 orders of magnitude further than previously achievable. He added that this distance is a practical starting point for building inter-city quantum networks.

If we ever want to establish a functional quantum internet, it is essential to distribute quantum entanglement between cities. An intercity quantum network would consist of distant network nodes of physical qubits that are entangled despite the large distance between them.

Dr. Sara Gamble, a manager of the Army program that sponsors the research, stated that this exhibit shows a significant step in the direction of realizing large scale distributed entanglement. She added that the quality of the entanglement (after traveling a considerable distance trough fiber optic cables) is high enough at the other end to meet a few of the conditions for some of the most challenging quantum networking functions.

The Innsbruck scientists their experiment with a calcium atom caught in an ion trap. Using laser beams, they wrote a quantum state onto the ion and simultaneously stimulated it to emit a photon in which quantum data is stored. As a consequence, the quantum states of the atom and the light particle were entangled. The difficulty lies in transferring the photon over fiber optic cables.

Dr. Lanyon stated that the photon released by the calcium ion had a wavelength of 854 nanometers and is quickly absorbed by the optical fiber. Consequently, the research team initially sent the light particle trough a nonlinear crystal illuminated by an intense laser. In doing so, the photon wavelength was changed into a value optimized for long-distance travel through optical fiber cables. The result was that after traveling 50 kilometers, the particles were still entangled.

It is still early days with regards to a worldwide quantum internet, but it is clear that scientists are making significant strides in this area.

Sources and further reading: Light-matter entanglement over 50 km of optical fiber / Quantium network / Quantum entanglement / U.S. Army Research Laboratory press release

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