TUM and MCQST Advance Quantum Communication With Photonic Crystal Waveguides

Christoph Hohmann / MCQST
Single-photon sources form the basis of quantum communication. Stephan Rinner and Florian Burger are developing nanostructures for this purpose that block unwanted frequencies, thereby significantly improving efficiency. In the experimental setup, laser light is guided through optical fibers to a microscope, where the tiny structures can be visualized.

(IN BRIEF) Researchers at the Technical University of Munich (TUM) and the Munich Center for Quantum Science and Technology (MCQST) have developed a new method to improve single-photon sources for quantum communication by using photonic crystal waveguides, nanostructures that suppress unwanted frequencies instead of amplifying the desired one. The approach addresses limitations of conventional resonators, which operate only within narrow frequency ranges and require precise tuning to individual photon sources. Initial experiments using erbium as the photon source increased the share of desired photons in emitted light from around 23 percent to approximately 72 percent, achieving results previously associated with more complex resonator methods. The method is also more scalable because multiple emitters can be used within one device and desired frequencies can be selected more flexibly, making it relevant for future quantum networks that need reliable interfaces to transfer information from quantum systems to individual photons and transmit them via optical fibres.

(PRESS RELEASE) MUNICH, 18-Aug-2026 — /EuropaWire/ — Researchers at the Technical University of Munich, known as TUM, and the Munich Center for Quantum Science and Technology, known as MCQST, have developed a new method to improve single-photon sources for quantum communication.

Quantum communication promises highly secure transmission of large volumes of data, but it depends on the ability to generate single photons reliably.

Producing these photons remains technically challenging, and previous approaches have faced limitations in scalability and precision.

The new method developed by the TUM and MCQST team uses nanostructures that block unwanted frequencies, significantly improving the efficiency of single-photon sources.

Single-photon sources form the foundation of quantum communication systems.

Researchers Stephan Rinner and Florian Burger are developing nanostructures for this purpose that suppress unwanted frequencies and improve photon generation.

In the experimental setup, laser light is guided through optical fibres to a microscope, allowing the tiny structures to be visualised.

The photonic crystal waveguides are only a few micrometers in size. They surround the emitter and thereby prevent the emission of photons at unwanted frequencies, ensuring that only photons of the required frequency are generated.

A different approach to photon control

Until now, researchers have mostly used resonators to produce single photons.

These tiny optical structures influence photon sources so that they emit light mainly at a specific frequency.

However, resonators work only within a narrow frequency range and must be precisely tuned to each photon source.

The TUM and MCQST researchers have developed a different approach.

Rather than amplifying emission at the desired frequency, they adapt the emitter’s environment so that less light is emitted at unwanted frequencies.

For this, the team uses photonic crystal waveguides.

These nanostructures contain regularly arranged patterns that block the pathways through which a photon source can emit light.

The researchers design the photonic crystal waveguides so that they suppress only unwanted light frequencies while preserving the desired ones.

The structures are only a few micrometres in size.

They surround the emitter and prevent the emission of photons at unwanted frequencies, helping ensure that photons are generated at the required frequency.

Threefold increase in the share of desired photons

Initial experiments confirmed the effectiveness of the new technology.

Using photonic crystal waveguides, the researchers increased the proportion of desired photons in emitted light from around 23 percent to approximately 72 percent.

This means the method achieves results that previously required much more complex resonator-based approaches.

The new approach also causes photon generation to occur slightly more slowly than before.

According to Andreas Reiserer, Professor of Quantum Networks at TUM, this can be an advantage for quantum communication.

He said that if photons are generated too quickly, controlling their properties becomes difficult.

For this reason, the new method is better suited for many emitters than resonators used to date.

The researchers carried out their first experiments using erbium as the photon source.

Erbium is already used in today’s fibre-optic technologies.

More scalable and adaptable than previous methods

Because photonic crystal waveguides offer broader bandwidth and greater flexibility than resonator-based systems, they provide two important advantages.

First, multiple photon sources, also known as emitters, can be used at the same time within a single device.

With resonators, this is possible only to a limited extent because of their very small size.

Second, the desired frequency can be selected more flexibly.

Unlike classical resonators, photonic crystal waveguides do not need to be precisely tuned to every individual emitter.

Florian Burger, doctoral student and first author of the publication, said future quantum networks are expected to connect many quantum systems with one another.

He said this will require interfaces that can reliably transfer information from a quantum system to individual photons and then transmit them, for example through optical fibres.

Burger said the team’s work lays the foundation for this development.

Publication and funding

The research was published in Nature Communications by Florian Burger, Stephan Rinner, Andreas Gritsch, Kilian Sandholzer and Andreas Reiserer.

The project was funded by the Federal Ministry of Education and Research, known as BMBF, and the Free State of Bavaria as part of the federal and state Excellence Strategy.

It also received funding from the High-Tech Agenda Bavaria.

The Chair of Quantum Networks is part of the TUM School of Natural Sciences.

Through the development of photonic crystal waveguides for single-photon sources, TUM and MCQST are advancing a more scalable approach to quantum communication technology, with potential applications in future quantum networks and fibre-optic information transmission.  

SOURCE: Technical University of Munich