Quantum Physics

Researchers use diamond nanostructures to take a significant step toward the quantum internet.

The use of diamond materials is crucial for cutting-edge technologies like the quantum internet. Special defect centers emit single light atoms known as single photons, which can be used as quantum bits (qubits) in quantum computing.

All photons must be collected in optical fibers and transmitted without being lost in order for data transmission in a quantum network to be possible at realistic communication rates over long distances. Furthermore, it is necessary to guarantee that each of these photons has the same color, i.e., identical frequency. Up until now, it has been impossible to meet these requirements.

The “Integrated Quantum Photonics” research team, led by Prof. Tim Schröder at Humboldt University in Berlin, has created and detected photons with stable photon frequencies that are emitted from quantum light sources or, more specifically, from nitrogen-vacancy defect centers in diamond nanostructures.

This was made possible by thoughtful diamond material selection, advanced nanofabrication techniques used at the Joint Lab Diamond Nanophotonics of the Ferdinand-Braun-Institut and Leibniz-Institut für Höchstfrequenztechnik, and precise experimental control protocols. Combining these techniques allows for the emission of photons at a constant (communication) frequency and a significant reduction in the electron noise that previously interfered with data transmission.

NV at night (regime 3). The center frequency of the ZPL resonance is extracted from Voigt fits (gray.s) when performing PLE scans, which are performed alternately with blocking the radiation for 60 s. (a) The shutter experiment A sample data set is displayed here. (b) The occurrence of spectral shifts discovered through the analysis of numerous data sets The extracted spectral diffusion value for “Laser on” corresponds to the spanned frequency range that was recorded over a period of 20 s. The spectral diffusion value for “Laser off” is obtained from the spectral difference between the final PLE scan performed before blocking the laser and the first scan performed after blocking the laser, as shown in panel (a). Submitted by Physical Review X in 2023 URL: 10.1103/PhysRevX.13.011042.

The Berlin researchers also demonstrate that, with the aid of the developed techniques, the existing communication rates between spatially separated quantum systems can potentially be increased by more than 1,000-fold, bringing the prospect of a future quantum internet one important step closer.

Individual qubits have been integrated into enhanced diamond nanostructures by the researchers. In order to transfer emitted photons into glass fibers in a targeted manner, these structures, which are 1,000 times thinner than a human hair, must be present.

However, atomic-level damage to the material surface occurs during the fabrication 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 a radio frequency that is unstable, making it impossible to perform successful quantum operations like entanglement.

The relatively high density of nitrogen impurity atoms in the crystal lattice of the diamond material used is one of its unique characteristics. These may 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. Zhu, asserts that “the precise physical processes need to be studied in more detail in the future.”. Tim Schröder is a dreg.

The statistical models and simulations developed and put into use by Dr. Gregor Pieplow from the same research group in collaboration with the experimental physicists support the conclusions reached from the experimental observations.

Physical Review X is the journal where the article appears.

More information: Laura Orphal-Kobin et al, Optically Coherent Nitrogen-Vacancy Defect Centers in Diamond Nanostructures, Physical Review X (2023). DOI: 10.1103/PhysRevX.13.011042

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