Stuttgart-Würzburg researchers develop novel single-photon source

04 Feb 2026

“Record-breaking” photons at telecom wavelengths made available on demand.

Nico Hauser (left) with other researchers from the Barz group.

A team of researchers of the University of Stuttgart and Julius-Maximilians-Universität Würzburg led by Stuttgart’s Prof. Stefanie Barz has demonstrated a source of single photons that combines on-demand operation with “record-high photon quality” in the telecommunications C-band.

”The lack of a high-quality on-demand C-band photon source has been a major problem in quantum optics laboratories for over a decade — our new technology now removes this obstacle,” said Prof. Barz.

When identical photons are made to act synchronously, the probability that certain measurement outcomes occur can be either boosted or decreased. Such quantum effects give rise to powerful new phenomena that lie at the heart of emerging technologies such as quantum computing and quantum networking. For these technologies to become feasible, high-quality interference between photons is essential.

Now Nico Hauser, scientist at Stuttgart and first author of the publication, and his colleagues have reported in Nature Communications a source of highly indistinguishable photons that is uniquely suitable for practical applications: it produces the photons on demand, and it operates at a wavelength compatible with existing telecommunications infrastructure.

Telecom challenge

For photonic quantum technologies to be scalable, they must integrate with the fiber-optic infrastructure that provides the backbone of today’s information-hungry society. In practice, this means that photon sources should operate in the telecommunications C-band around a wavelength of 1550 nm, where optical losses in silica fibres are lowest.

This requirement has long posed a challenge: while photon sources based on so-called quantum dots—nanostructures that function like artificial atoms—have achieved near-ideal photon properties for emission at shorter wavelengths (780–960 nm), extending these results to the telecom regime proved difficult.

The most practical alternative, known as spontaneous parametric down-conversion (SPDC), produces high-quality photons but does so probabilistically. That is, it is not possible to predict when exactly a desired photon is produced. This makes it impossible to synchronize multiple photons from different sources for protocols that need them simultaneously.

By contrast, so-called deterministic sources produce a photon whenever they are triggered. Quantum-dot devices exist for C-band photons; however, they achieved two-photon interference visibilities—a measure of indistinguishability—of around 72% at best. This is well below what SPDC sources routinely deliver and insufficient for demanding quantum protocols. “Our new device now lifts this roadblock,” said Stefanie Barz.

Inside the quantum optics laboratory at the University of Stuttgart.

Toward scalable photonic systems

The new photon source developed by Hauser’s group consists of indium arsenide quantum dots embedded within indium aluminium gallium arsenide and integrated into a circular Bragg grating resonator, which enhances photon emission.

The team systematically compared different schemes for triggering emission and found that harnessing excitations mediated by elementary vibrations in the crystal lattice—rather than pumping the quantum dots with higher-energy light—yielded the best results. In this mode, they achieved a raw two-photon interference visibility of nearly 92%, the highest reported for any deterministic single-photon source in the telecom C-band.

“Our ability to simultaneously achieve deterministic single-photon generation, emission in the telecom C-band, and high photon indistinguishability will now enable applications that require large numbers of synchronized photons, from measurement-based quantum computing to quantum repeaters for long-distance communication,” said Hauser.

The Stuttgart and Würzburg teams, led by Prof. Sven Höfling, are working within the PhotonQ project, a consortium funded by the German Federal Ministry of Research, Technology and Space. Led by Prof. Barz, it is working to build the foundations for a new type of practical photonic quantum processor for quantum computing.