The group produced the crystals themselves and integrated them into so-called III-V photonics platforms.University of Würzburg
German scientists have laid the groundwork for the next generation of quantum technologies by developing an ultra-fast, ultra-low-loss optical phase modulator that could enable scalable quantum photonic circuits.
The research team at Julius Maximilian University of Würzburg (JMU) tackled one of quantum computing’s toughest challenges by discovering a way to precisely control quantum light without destroying the fragile information it carries.
Backed by more than USD 7.7 million (EUR 6.6 million) from the Federal Ministry of Research, Technology, and Space (BMFTR), the revolutionary project was led by Andreas Pfenning, PhD, a professor who heads the Ferro35 junior research group at the university physics department.
The new chip, capable of controlling light signals at extremely high speeds with almost no losses, could reportedly speed up the transition of quantum photonics from laboratory experiments to practical, large-scale technologies.
Controlling quantum light
In classical fiber-optic networks, optical phase modulators are standard parts that encode information onto light by altering its phase at extremely high speeds. But quantum technologies operate under stricter conditions, since even tiny optical losses or excess noise can collapse quantum states.
“We need components that combine very high speeds with extremely low optical losses,” Pfenning reported. “This combination does not yet exist, and it is essential for complex quantum circuits.”
To tackle the issue, Pfenning and his team pursued a new approach by integrating barium titanate (BTO), a ferroelectric material with outstanding electro-optic traits, into III-V photonics platforms, which are widely used to generate quantum light on chips.
To maintain the purity required for ferroelectric behavior, the group then grew its own crystals in-house. The method, also known as molecular beam epitaxy (MBE) is one of the most precise thin-film fabrication techniques in materials research.
“For ferroelectric materials, we need an exceptionally clean process environment,” Pfenning explained. “Even the smallest impurities can alter the properties of the crystals.”
The researchers carried out the project in ultra-high-vacuum cleanrooms at the Gottfried Landwehr Laboratory for Nanotechnology. An additional system is currently being installed to specifically support the research activities of the Ferro35 group.
Scalable quantum chips
In addition to the phase modulator, the team is building a full toolkit for photonic quantum circuits, including waveguides, couplers, and integrated quantum light sources. Each component is first simulated, then fabricated, and finally tested.
“We are building a component library that allows us to design, assemble, and directly manufacture circuits,” Pfenning noted. “In a way, it’s like building with Lego bricks: if the right element is placed in the right position, a functional circuit gradually emerges.”
According to the professor, the resulting designs can be tested experimentally without delay. This modular strategy also opens the door for hands-on education. It allows students to design and test quantum photonic layouts in a realistic research environment.
While fully scalable quantum computers remain years away, the new technology could find near-term applications. High-speed, low-loss modulators are in strong demand for advanced telecommunications and optical signal processing.
“Fast, low-loss modulators are also of great interest for telecommunications,” Pfenning concluded in a press release. “Our technology could provide important impulses here as well.”
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