At a temperature of 4 degrees Kelvin, many electro-optic materials struggle to maintain performance. However, the nanoelectronics research center imec has successfully created a thin film of strontium titanate (SrTiO3) that showcases unprecedented electro-optic capabilities with minimal optical loss. This breakthrough suggests the potential for shorter and quicker components in quantum devices.
Quantum computers and detectors often operate at temperatures nearing absolute zero. In such extreme environments, even the most effective materials at room temperature face challenges in efficiently managing light. This ability is crucial for encoding, routing, and transforming information in electro-optic networks, which are currently utilized in data and telecommunications but are increasingly relevant for ultra-low temperature quantum connections.
A recent publication in the journal Science details how researchers from imec, collaborating with KU Leuven and Ghent University, have modified a widely used crystal, strontium titanate (SrTiO3), to achieve record-breaking performance at cryogenic temperatures. The research team, led by Christian Haffner and including Ph.D. candidates Anja Ulrich, Kamal Brahim, and Andries Boelen, reported an effective Pockels coefficient nearing 350 pm/V at 4 K, the highest recorded for any thin-film electro-optic material at this temperature.
The Pockels coefficient quantifies how a material”s refractive index alters in response to an electric field. A higher Pockels coefficient indicates greater efficiency in light modulation per volt. While most materials see a decline in effectiveness at ultra-low temperatures, the engineered SrTiO3 thin film exhibits improved performance, allowing for the development of smaller, faster electro-optic components.
Moreover, this advancement is achieved with minimal optical losses. In practical terms, the combination of high electro-optic strength and low loss enables the creation of smaller devices that conserve more photons, a critical aspect for quantum systems. Haffner stated, “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.” He emphasized that this illustrates how atomic-scale materials engineering can lead to significant breakthroughs at the device level.
The long-term implications of this foundational research are evident. The provision of a cryogenic-ready electro-optic material with exceptional thin-film performance accelerates the progress of next-generation quantum interconnects, modulators, and transducers, which could ultimately connect superconducting processors with optical networks.
Additionally, the findings are published alongside another study that demonstrates that fine-tuning strontium titanate can enhance its response to electric fields at temperatures between 4 K and 5 K, making it remarkably strong and adjustable. Although this second study was conducted by a team from Stanford University, imec researchers contributed to both studies.
Together, these papers illustrate the extent to which the performance of strontium titanate can be enhanced and controlled, as well as the techniques for constructing low-loss, wafer-scale thin films suitable for photonic chip production. The first authors noted, “This project demanded tight control over how the film was grown, expert wafer bonding, and high-precision testing at cryogenic temperatures… A true cross-disciplinary effort. We are excited that our fundamental discovery can now seed new device concepts for quantum photonics.”
