Quantum internet researched by U.S. Army

RESEARCH TRIANGLE PARK, N.C. The U.S. Army's Combat Capability Development's Army Research Laboratory's Center for Distributed Quantum Information saw researchers at the University of Innsbruck achieve a record for the transfer of quantum entanglement between matter and light — a distance of 50 kilometers using fiber optic cables. Such an internet could offer the military security, sensing, and timekeeping capabilities not possible with traditional networking approaches.

Photo courtesy of IQOQI Innsbruck.

Beginning with a calcium atom trapped in an ion trap, researchers then used laser beams and wrote a quantum state onto the ion and excited it to emit a photon in which quantum information is stored. As a result, the quantum states of the atom and the light particle were entangled.

Intercity quantum networks would be composed of distant network nodes of physical qubits, which are entangled. This distribution of entanglement is essential for establishing a quantum internet, researchers said. The challenge is to transmit the photon over fiber optic cables. Researchers therefore initially sent the light particle through a nonlinear crystal illuminated by a strong laser.

The photon wavelength was converted to the optimal value for long-distance travel. The researchers then sent this photon through the 50-kilometer-long optical fiber line. Their measurements show that atom and light particles were still entangled even after the wavelength conversion and the distance traveled.