Fluorescence from a single ion [circled in red] reveals how individual photons can now be controlled and emitted using standard fiber optic materials operating at room-temperature. KAORU SANAKA/TUS
Unlocking the Potential of a Cost-Effective Quantum Internet
In the ever-evolving landscape of quantum technology, the quest for a room temperature single-photon light source has long been a pivotal pursuit. Now, a groundbreaking collaboration between researchers at Tokyo University of Science (TUS) and the Okinawa Institute of Science and Technology has birthed a prototype that could redefine the possibilities of quantum networking. Their innovation, outlined in a recent issue of Physical Review Applied, introduces a novel approach using standard materials, sidestepping the complexity and cost associated with previous methods.
The Quest for Single-Photon Emission at Room Temperature
Producing single photons at room temperature is a game-changer for the realization of a quantum internet and the advancement of practical quantum computers. These single photons act as quantum bits (qubits), the fundamental building blocks of quantum computing. Traditional methods involve intricate engineering using materials like doped carbon nanotubes or demanding cryogenic conditions, making them costly and challenging.
However, the collaborative team from TUS and the Okinawa Institute of Science and Technology has disrupted the status quo with their groundbreaking prototype, showcasing a cost-effective and accessible room temperature single-photon light source.
The Game-Changing Emitter: Amorphous Silica Optical Fiber
The magic lies in the unassuming amorphous silica optical fiber, readily available in the market. The researchers pre-doped the fiber with optically active rare earth (RE) ytterbium ions, turning an ordinary cable into an extraordinary single-photon emitter. The fabrication process involves a conventional technique called heat-and-pull, where the fiber is heated and stretched using a programmable stepping motor, gradually reducing its core diameter and creating a controlled taper.
Kaoru Sanaka, the lead researcher at TUS, emphasizes the simplicity of their approach, stating, "Our single-photon light source is low cost, not so technically complex, and it can be fabricated at room temperatures. This eliminates the need for expensive cooling systems and increases the potential to create quantum networks—a quantum internet—that are cost-effective and accessible."
Embracing Room Temperature Efficiency
Unlike conventional methods that embed quantum particles into the outside of a tapered fiber, the team's approach involves embedding and aligning RE ions inside the fiber's core during manufacturing. This optimization enhances the structural capture and channeling of emitted photons, maximizing efficiency.
The heat-and-pull tapering procedure further stretches the spacing between individual ytterbium ions, effectively transforming them into single-photon emitters. Sanaka explains, "The average distance of about 30 microns between distributed single RE atoms is much larger than the optical diffraction limit. So it’s possible to extract the photons emitted from each spatially isolated RE ion."
Looking to the Future: Scaling and Commercialization
While this room temperature single-photon source approach has been explored before, previous efforts faced scalability challenges. Sanaka acknowledges this and reveals their plans to test other RE elements, with erbium-doped fiber next in line. The team is also working on increasing the quantity of emitted photons and improving their quality and emission speed.
To achieve this, the researchers are delving into the realm of micro- or nano-scale cavities. These tiny spaces, when introduced near or on the surface of the emitters, act as resonators for the photons, enabling a more controlled and concentrated release of light. The incorporation of such cavities is poised to enhance the indistinguishability of emitted photons, a crucial step toward applications like quantum communications and quantum computations.
Sanaka concludes optimistically, "By successfully combining cavities with our emitters, we may then be in a position to consider commercialization of the technology." The collaboration between TUS and the Okinawa Institute of Science and Technology marks a significant stride toward democratizing quantum networking, making it more accessible and cost-effective than ever before. As we witness the fusion of standard materials with quantum innovation, the future of a quantum internet is undoubtedly brighter.
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