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Secure Quantum Communication Single-Photon Source for the Future Quantum Internet

From Hendrik Härter | Translated by AI 3 min Reading Time

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Japanese researchers have developed a method in which a cost-effective single-photon source is directly integrated into the optical fiber. This is intended to enhance communication security and eliminate the need for expensive cryogenic systems.

Researchers from Japan are working on integrating a single-photon source directly into the optical fiber. This makes it possible to use standard optical fibers.(Image: freely licensed / Pixabay)
Researchers from Japan are working on integrating a single-photon source directly into the optical fiber. This makes it possible to use standard optical fibers.
(Image: freely licensed / Pixabay)

With the increasing computational power of quantum computers, classical cryptographic methods are coming under pressure. In particular, asymmetric algorithms such as RSA or ECC could be broken through quantum algorithms (e.g., Shor's algorithm). To ensure long-term data security, researchers are working on quantum communication systems that rely on physically secure information transmission.

A central element of such systems is the single-photon source, which provides defined photon packets for quantum key distribution (QKD) methods. Crucial for practical use is low-loss coupling of photons into standard optical fibers, as any optical attenuation reduces the range and efficiency of the quantum connection.

So far, single-photon sources have mostly been implemented outside the optical fiber, for example, with quantum dots or rare earth ions in solid-state matrices. However, this construction resulted in high coupling losses, as only a small fraction of the emitted photons entered the fiber's input mode. For a practical quantum network architecture, high coupling and channeling efficiencies are therefore essential.

Fiber-Coupled Single-Photon Source

The proposed method uses a single rare earth ion in a tapered optical fiber to generate single photons directly and guide them within the fiber. This is an important, cost-effective component for future quantum communication.(Image: Dr. Kaoru Sanaka from Tokyo University of Science, Japan.)
The proposed method uses a single rare earth ion in a tapered optical fiber to generate single photons directly and guide them within the fiber. This is an important, cost-effective component for future quantum communication.
(Image: Dr. Kaoru Sanaka from Tokyo University of Science, Japan.)

In a study, a research team led by Associate Professor Kaoru Sanaka from the Tokyo University of Science (TUS) in Japan has now found a solution: they developed a highly efficient fiber-coupled single-photon source where the photons are generated directly within the fiber. Prof. Sanaka explains: "In our approach, a single isolated RE ion, enclosed in a tapered optical fiber, is selectively excited by a laser to generate single photons."

Researchers propose a system for generating single photons at room temperature. For this, they selectively excite an isolated Nd³⁺ ion in an optical tapered fiber.(Image: Dr. Kaoru Sanaka from Tokyo University of Science, Japan.)
Researchers propose a system for generating single photons at room temperature. For this, they selectively excite an isolated Nd³⁺ ion in an optical tapered fiber.
(Image: Dr. Kaoru Sanaka from Tokyo University of Science, Japan.)
Scientists have succeeded in generating photons at room temperature using a single neodymium ion (Nd³⁺). This could potentially impact quantum communication technology. Image (a) shows the spatially resolved single Nd³⁺. Image (b) shows the autocorrelation measurement function of Nd³⁺ achieved through selective excitation.(Image: Dr. Kaoru Sanaka from Tokyo University of Science, Japan.)
Scientists have succeeded in generating photons at room temperature using a single neodymium ion (Nd³⁺). This could potentially impact quantum communication technology. Image (a) shows the spatially resolved single Nd³⁺. Image (b) shows the autocorrelation measurement function of Nd³⁺ achieved through selective excitation.
(Image: Dr. Kaoru Sanaka from Tokyo University of Science, Japan.)

The team also included doctoral student Kaito Shimizu, Assistant Professor Tomo Osada from TUS, and Associate Professor Mark Sadgrove. Their results were published in the journal Optics Express.

The researchers used a silicon fiber doped with neodymium ions (Nd³⁺), which is versatile in telecommunications due to its emission properties in the near-infrared around 41.70 microinches. Through a thermal tapering process, the fiber was thinned to selectively excite the Nd³⁺ ions.

This led to a novel method in which "single Nd³⁺ ions were selectively excited with a pump laser at room temperature to generate single photons directly in the guided mode of the fiber," explains Prof. Sanaka further.

This innovative approach enables cost-effective and straightforward integration into existing systems through the use of commercially available optical fibers. Additionally, the need for expensive cryosystems is eliminated, as the system operates at room temperature. Prof. Sanaka emphasizes: "Our method allows for the highly efficient transmission of single photons from the source to the target." These features make it a promising candidate for the next generation of quantum-based networks.

From the perspective of high-frequency and photonics development, this approach offers several advantages:

  • Integrability: Utilizing standard optical fibers simplifies HF layout and system integration.
  • Scalability: Multi-channel structures with multiple ions within a fiber are conceivable, enabling photonic multi-qubit systems.
  • Signal Integrity: Direct waveguide coupling minimizes reflection and loss points, which is relevant for precise synchronization and timing systems in the GHz range.

The method could be used not only for quantum communication systems but also for quantum computing applications. By operating multiple isolated ions within a fiber, enhanced multi-qubit processors can be developed.

Future Research Beyond Quantum Communication

Future research should focus on further optimizing the photon wavelength to enable practical applications in spectroscopy and imaging analysis. In the long term, this technology could be used not only for quantum communication networks but also for spectrally selective measurement techniques, optical clock distribution systems, and photonic computing architectures. Overall, this development in single-photon sources marks a significant advancement for practical quantum technologies and paves the way for secure, eavesdropping-proof communication networks. (heh)

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