Single photon room temperature light source for quantum processing
Researchers in Japan have developed an ytterbium-doped optical fibre that works at room temperature for cost-effective photonic quantum applications.
Single-photon emitters quantum mechanically connect quantum bits (or qubits) between nodes in quantum networks. They are typically made by embedding rare-earth elements in optical fibres at extremely low temperatures.
The team, led by Associate Professor Kaoru Sanaka from Tokyo University of Science, have
Quantum-based systems promise faster computing and stronger encryption for computation and communication systems. These systems can be built on fiber networks involving interconnected nodes which consist of qubits and single-photon generators that create entangled photon pairs.
The rare-earth (RE) atoms and ions in solid-state materials are compatible with fibre networks and emit photons across a broad range of wavelengths. The wide spectral range means the doped optical fibre can be used in various applications, such as free-space telecommunication, fibre-based telecommunications, quantum random number generation, and high-resolution image analysis. However, so far, single-photon light sources have been developed using RE-doped crystalline materials at cryogenic temperatures, which limits the practical applications of quantum networks based on them.
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“Single-photon light sources are devices that control the statistical properties of photons, which represent the smallest energy units of light,” said Dr. Sanaka. “In this study, we have developed a single-photon light source using an optical fiber material doped with optically active RE elements. Our experiments also reveal that such a source can be generated directly from an optical fiber at room temperature.”
To fabricate the ytterbium-doped optical fibre, the researchers tapered a commercially available ytterbium-doped fibre using a heat-and-pull technique, where a section of the fibre is heated and then pulled with tension to gradually reduce its diameter.
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Within the tapered fibre, individual RE atoms emit photons when excited with a laser. The separation between these RE atoms plays a crucial role in defining the fibre’s optical properties. For instance, if the average separation between the individual RE atoms exceeds the optical diffraction limit, which is determined by the wavelength of the emitted photons, the emitted light from these atoms appears as though it is coming from clusters rather than distinct individual sources.
The researchers employed an analytical method known as autocorrelation, which assesses the similarity between a signal and its delayed version. By analyzing the emitted photon pattern using autocorrelation, the researchers observed non-resonant emissions and further obtained evidence of photon emission from the single ytterbium ion in the doped filter.
The developed optical fibre with ytterbium atoms can be manufactured without the need for expensive cooling systems. This overcomes a significant hurdle and opens doors to various next-generation quantum information technologies.
“We have demonstrated a low-cost single-photon light source with selectable wavelength and without the need for a cooling system. Going ahead, it can enable various next-generation quantum information technologies such as true random number generators, quantum communication, quantum logic operations, and high-resolution image analysis beyond the diffraction limit,” said Sanaka.