Researchers have successfully engineered a thin-film version of a common crystal, strontium titanate, to exhibit unprecedented electro-optic performance at the frigid temperatures required for quantum computing. A team at the nanoelectronics research center imec, in collaboration with Belgian universities, has overcome a critical bottleneck in quantum technologies, where controlling light efficiently near absolute zero has been a persistent challenge. The breakthrough unlocks the potential for smaller, faster, and more energy-efficient components to route and process information in next-generation quantum systems.
This development, detailed in the journal Science, is significant because most materials that excel at modulating light at room temperature become ineffective in the cryogenic conditions that quantum computers and detectors demand. The imec-led team not only found a material that works well at 4 Kelvin but discovered that its performance paradoxically improves in the extreme cold. By transforming the atomic structure of strontium titanate (SrTiO₃), they achieved a record-high efficiency in converting electronic signals to optical ones, a crucial function for linking quantum processors with fiber-optic networks. This materials engineering feat paves the way for integrated photonic circuits that are essential for scaling up quantum hardware.
Overcoming Cryogenic Limitations
The world of quantum computing operates on principles fundamentally different from classical computers, relying on the fragile quantum states of subatomic particles. To maintain these delicate states and prevent them from being disturbed by thermal noise, quantum processors must be cooled to temperatures just a few degrees above absolute zero, or around -270 degrees Celsius (-450 degrees Fahrenheit). This extreme environment poses a major engineering hurdle for all the components that must operate alongside the quantum bits, or qubits. One of the most significant challenges is managing the flow of information into and out of the quantum processor.
Information in these systems is often encoded and transmitted using photons, or particles of light. This requires electro-optic materials that can alter the properties of light, such as its phase or polarization, in response to an electrical voltage. Such materials form the basis of modulators, switches, and interconnects that translate electrical data from the quantum core into optical signals that can travel over fiber-optic cables. At room temperature, materials like lithium niobate are widely used for this purpose in telecommunications. However, the physical properties of these materials degrade severely at cryogenic temperatures, rendering them largely ineffective. This limitation has forced engineers to use bulky, inefficient components, hindering the development of compact and scalable quantum systems.
A New Record in Electro-Optic Efficiency
The research team focused its efforts on strontium titanate (SrTiO₃), a well-known oxide material. In its bulk form, SrTiO₃ does not exhibit the desired electro-optic properties at low temperatures. However, the researchers discovered that by fabricating it as a thin film and carefully engineering its crystalline structure, its behavior could be dramatically altered. The key metric for performance in this context is the Pockels coefficient, which quantifies how strongly a material’s refractive index—the degree to which it bends light—changes when an electric field is applied. A higher Pockels coefficient allows for smaller devices that can operate at higher speeds and with lower power consumption.
Redefining Material Properties
Through a process of atomic-scale materials engineering, the team coaxed the SrTiO₃ thin film into a state not typically observed in nature. They effectively transformed it from a “quantum paraelectric” material into a “cryo-ferroelectric” one. This structural change at low temperatures unlocked a massive Pockels effect that was previously unexpected in this material. The team, led by corresponding author Christian Haffner and spearheaded by Ph.D. students Anja Ulrich, Kamal Brahim, and Andries Boelen, reported an effective Pockels coefficient of nearly 350 picometers per volt (pm/V) at a temperature of 4 Kelvin. This value represents the highest figure ever reported for any thin-film electro-optic material at this temperature, shattering previous records and establishing SrTiO₃ as a leading candidate for cryogenic applications.
Low Loss, High Impact
Just as important as the high Pockels coefficient is the material’s low optical loss. In quantum systems, every single photon can carry critical information, so it is essential to minimize any loss as light travels through a component. The engineered SrTiO₃ film demonstrated excellent transparency, ensuring that photons are not wasted. This combination of high efficiency and low loss is the holy grail for building practical quantum photonic devices. It means that modulators and other components can be made significantly smaller and can operate with much lower voltages, reducing heat dissipation—a critical concern inside a cryogenic environment. Smaller devices also mean that more can be packed onto a single chip, a key requirement for building complex quantum circuits.
Building Blocks for Quantum Networks
The practical implications of this research are far-reaching. The ability to create compact, high-performance electro-optic components that work at 4 Kelvin directly addresses a critical integration challenge in the quantum field. Superconducting qubits, one of the leading technologies for quantum processors, operate at these temperatures. However, to connect multiple quantum computers or to link them to a future quantum internet, information must be converted into optical signals that can travel long distances with minimal loss. This new material provides a powerful tool for creating the transducers and interconnects needed to bridge the gap between superconducting processors and optical communication networks.
The work represents a collaboration between imec, a global research and development hub in nanoelectronics, and the universities of KU Leuven and Ghent University. This interdisciplinary effort combined expertise in materials science, thin-film deposition, and cryogenic testing. Researchers note that the developed processes are compatible with wafer-scale manufacturing techniques used in the semiconductor industry. This suggests a clear path toward producing these high-performance SrTiO₃ thin films on photonic chips in a scalable and reproducible manner, moving the technology from a laboratory curiosity to a manufacturable solution.
Future of Cryogenic Photonics
This fundamental materials science breakthrough seeds a new generation of device concepts for quantum photonics. By demonstrating that a common material like strontium titanate can be engineered to outperform all other contenders in the extreme cold, the research opens up a new avenue for material discovery. Scientists can now explore similar techniques with other oxide materials to unlock novel properties tailored for specific cryogenic applications, including quantum sensing and detection.
The long-term vision is an integrated ecosystem where quantum processors, memory, and communication links are all built on a unified platform. The development of a robust, chip-scale electro-optic modulator for cryogenic temperatures is a foundational step in that direction. As the field of quantum technology continues to advance, the ability to efficiently manipulate and transmit quantum information will become increasingly critical. This work on strontium titanate provides a vital new component for the quantum engineer’s toolkit, accelerating the quest to build powerful and interconnected quantum systems.
