​Scientists are One Step Closer to Quantum Internet

A team of researchers from the Humboldt-Universität zu Berlin and the Ferdinand-Braun-Institut (Germany) has succeeded in generating photons with stable frequencies emitted from quantum light sources.

“Diamond material is of great importance for future technologies such as the quantum internet,” said senior author Professor Tim Schröder from the Humboldt-Universität zu Berlin and his colleagues. “Special defect centers can be used as qubits and emit single light particles that are referred to as single photons.” “To enable data transmission with feasible communication rates over long distances in a quantum network, all photons must be collected in optical fibers and transmitted without being lost.” “It must also be ensured that these photons all have the same color, i.e., the same frequency.” “Fulfilling these requirements has been impossible — until now.”

In their research, the authors were able to generate and detect photons with stable photon frequencies emitted from quantum light sources, or, more precisely, from nitrogen-vacancy defect centers in diamond nanostructures. “This was enabled by carefully choosing the diamond material, sophisticated nanofabrication methods, and specific experimental control protocols,” they said. “By combining these methods, the noise of the electrons, which previously disturbed data transmission, can be significantly reduced, and the photons are emitted at a stable (communication) frequency.”

The team’s results show that current communication rates between spatially separated quantum systems can prospectively be increased more than 1,000-fold — an important step closer to a quantum internet. “We integrated individual qubits into optimized diamond nanostructures,” they said. “These structures are 1,000 times thinner than a human hair and make it possible to transfer emitted photons in a directed manner into glass fibers.” “However, during the fabrication of the nanostructures, the material surface is damaged at the atomic level, and free electrons create uncontrollable noise for the generated light particles.” “Noise, comparable to an unstable radio frequency, causes fluctuations in the photon frequency, preventing successful quantum operations such as entanglement.”

“A special feature of the diamond material used is its relatively high density of nitrogen impurity atoms in the crystal lattice.” “These possibly shield the quantum light source from electron noise at the surface of the nanostructure.” “However, the exact physical processes need to be studied in more detail in the future,” said first author Dr. Laura Orphal-Kobin, also from the Humboldt-Universität zu Berlin.