The use of diamond materials is crucial for cutting-edge technologies like the quantum internet. Special defect centres emit single light particles known as single photons and can be employed as quantum bits (qubits).
All photons must be gathered in optical fibres and transported without being lost in order for data transmission in a quantum network to be possible at realistic communication rates across long distances. The same hue, or frequency, of each of these photons must also be guaranteed. Up until now, it has been difficult to meet these conditions.
For the first time ever, scientists from Humboldt-Universität zu Berlin’s “Integrated Quantum Photonics” group, led by Prof. Dr. Tim Schröder, have generated and detected photons with stable photon frequencies emitted from quantum light sources, or, more precisely, from nitrogen-vacancy defect centres in diamond nanostructures.
This was made possible through the thoughtful selection of the diamond material, advanced nanofabrication techniques used at the Joint Lab Diamond Nanophotonics of the Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik, and precise experimental control protocols. Combining these techniques allows for a large reduction in the electron noise that previously interfered with data transmission and a steady (communication) frequency for the photons.
Additionally, the Berlin researchers demonstrate that the discovered techniques can potentially boost the existing communication speeds between spatially dispersed quantum systems by more than 1,000-fold, which represents a significant advancement towards a potential quantum internet.
Individual qubits have been incorporated by the researchers into enhanced diamond nanostructures. These structures allow for the guided transmission of radiated photons into glass fibres and are 1,000 times thinner than a human hair.
However, atomic level damage to the material surface occurs during the creation of the nanostructures, and uncontrolled noise from free electrons is produced for the produced light particles. The photon frequency fluctuates due to noise, which is like an unstable radio frequency and prevents successful quantum activities like entanglement.
The relatively high density of nitrogen impurity atoms in the crystal lattice of the diamond material employed is one of its unique characteristics. These might provide protection from electron noise at the nanostructure’s surface for the quantum light source. However, Laura Orphal-Kobin, who studies quantum systems alongside Prof. Dr. Tim Schröder, notes that future research must focus more on the precise physical processes.
The statistical models and simulations that Dr. Gregor Pieplow from the same research group is creating and using in conjunction with the experimental physicists provide support for the results reached from the experimental observations.
