Light storage in light cages: A revolutionary approach to on-chip quantum memories

Quantum information storage is a cornerstone technology for the emerging quantum internet and quantum computation. While current quantum communication networks face fundamental limitations due to signal loss over long distances, quantum memories offer a promising solution by enabling quantum repeaters that can extend the range of quantum networks through entanglement swapping operations.

 

In a breakthrough published in Light: Science & Applications, a research team led by scientists from the Humboldt-Universität zu Berlin, the Leibniz Institute of Photonic Technology, and the University of Stuttgart has demonstrated a revolutionary approach to quantum memories using novel 3D-nanoprinted structures called "light cages" filled with atomic vapor. The combination of confining light and atoms on a chip represents a transformative approach in quantum memory technologies, offering scalability and integration capabilities for quantum photonic systems.

 

Light Cage Technology

The light cages are specialized hollow-core waveguides that combine the advantages of light confinement with unique side-wise access to their core regions. Unlike traditional hollow-core fibers that require months to fill with atomic vapor, these nanoprinted structures allow rapid diffusion of cesium atoms, reducing filling times from months to just days while maintaining excellent optical field confinement.

 

The fabrication process employs two-photon polymerization lithography using commercial 3D printing systems, enabling the precise creation of complex hollow-core waveguide structures directly on silicon substrates. To ensure long-term stability in the reactive cesium environment, the structures are coated with a protective layer, demonstrating remarkable durability with no degradation observed even after five years of operation.

 

“We created a guiding structure that allows quick diffusion of gases and fluids inside its core, with the versatility and reproducibility provided by the 3D-nanoprinting process. This enables true scalability of this platform, not only for intra-chip fabrication of the waveguides but also inter-chip, for producing multiple chips with the same performance,” explained the research team.

 

Performance as Quantum Memory

The light cages enable highly efficient conversion of guided light pulses into collective atomic excitations. After a chosen storage period, an optical control laser can reverse the process, releasing the stored light on demand. In a key milestone, the team successfully stored attenuated light pulses containing only a few photons for durations of several hundred nanoseconds. Looking ahead, the researchers are optimistic about extending this capability to the storage of single photons for many milliseconds.

 

A most significant achievement for application in scalable quantum technology was the successful integration of multiple light cage memories onto a single chip within a cesium vapor cell. The team demonstrated that different light cages with identical geometrical parameters exhibit nearly identical storage performance for two different devices on the same chip.

 

This reproducibility stems from the exceptional precision of the 3D-nanoprinting process, which achieves intra-chip structure variations of less than 2 nanometers and inter-chip variations of less than 15 nanometers. Such consistency is crucial for the spatial multiplexing concept that could revolutionize quantum memory integration.

 

Impact and Future Prospects

The light cage quantum memory platform addresses critical challenges in quantum technologies. In quantum repeater networks, these memories could enable parallel single-photon synchronization, dramatically improving the efficiency of long-distance quantum communication. For photonic quantum computing, they offer controllable delays necessary for feed-forward operations in measurement-based quantum computing architectures.

 

The compact size and room-temperature operation of the system provide significant practical advantages over competing technologies that require cryogenic cooling or complex atomic trapping systems. The platform operates at slightly above room temperature, excelling in practicality with higher bandwidths per memory mode compared to alternative approaches. The ability to fabricate multiple quantum memories on a single chip with reproducible performance characteristics opens the door to large-scale quantum photonic integration. The versatility of the fabrication process, combined with the potential for direct fiber coupling and integration with existing photonic technologies, positions light cage memories as a key enabling technology for future quantum networks.

 

The development of light cage quantum memories represents a major step forward in quantum photonic technology. By combining advanced 3D-nanoprinting techniques with fundamental quantum optics principles, the researchers have created a scalable platform that could accelerate the development of quantum communication networks and quantum computing systems.

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