imec breaks performance record in super-cooled thin-film strontium titanate

03 Nov 2025

Breakthrough in material engineering “accelerates the roadmap for quantum applications”.

Quantum computers and detectors run at temperatures close to absolute zero. In these extreme conditions, even the best room temperature materials struggle to control light efficiently. This feature is essential to encode, route, and convert information in electro-optic networks, which at room temperature are used in data and telecom applications, but also increasingly for ultra-low temperature quantum links.

Researchers at imec, Leuven, Belgium, in collaboration with KU Leuven and Ghent University, have re-engineered a common crystal, strontium titanate (SrTiO₃) so it behaves with record performance at cryogenic temperatures.Their work is described in Science.

The research team, led by Christian Haffner alongside PhD students Anja Ulrich, Kamal Brahim, and Andries Boelen, has demonstrated an effective Pockels coefficient of close to 350 pm/V at 4 K, the highest reported for any thin-film electro optic material at this temperature.

The Pockels coefficient measures how strongly a material’s refractive index changes when an electric field is applied. The larger the Pockels coefficient, the more efficiently the light can be modulated per volt. At ultra-low temperatures, most materials get weaker, but the engineered SrTiO₃ thin film does the opposite, enabling shorter, faster electro-optic components.

Limited losses

Crucially, the team achieves this performance with limited optical losses. In practical terms, that combination of high electro-optic strength with low loss, means scientists can build smaller devices that waste fewer photons, which is essential for quantum systems.

“By converting a quantum paraelectric into a cryo ferroelectric thin film, we reveal a powerful Pockels effect where none was expected. This opens a new materials lane for compact, low loss electro optic components at 4 degrees Kelvin,” said Haffner, corresponding author at imec. “It’s a great example of how materials engineering at the atomic scale can unlock device level breakthroughs.”

The long-term value of this fundamental research is clear: by providing a cryogenic ready electro optic material with record performance in thin film form, the work accelerates the development of next generation quantum interconnects, modulators, and transducers that could eventually bridge superconducting processors and optical networks.

Two studies

The results are published back-to-back with another study showing that, by carefully tuning strontium titanate, its response to electric fields at 4 to 5 K can be made extremely strong and adjustable. While the second study was led by a Stanford research team, imec researchers contributed to both advances. Combined, both papers show how far strontium titanate’s performance can be pushed and controlled, and how to build it into low-loss, wafer-scale thin films suitable for the production of photonic chips.

This achievement reflects imec’s tenure track model of backing bold, long-horizon research: protected time, access to advanced fabrication, and cross-disciplinary support that turn early scientific insights into future technology platforms.

“This project demanded tight control over how the film was grown, expert wafer bonding, and high-precision testing at cryogenic temperatures – a cross-disciplinary effort,” said first authors Anja Ulrich, Kamal Brahim and Andries Boelen. “We’re excited that our fundamental discovery can now seed new device concepts for quantum photonics.”