11/26/2025 Jeni Bushman
Physicists in Illinois Grainger Engineering have reported the first demonstration of a slow-light effect on photonic chips. Their findings have implications for quantum light storage and manipulation.
Written by Jeni Bushman
Integrated circuits are the brains behind modern electronic devices like computers or smart phones. Traditionally, these circuits — also known as chips — rely on electricity to process data. In recent years, scientists have turned their attention to photonic chips, which perform similar tasks using light instead of electricity to improve speed and energy efficiency.
In a recent advancement for the field, physicists from The Grainger College of Engineering at the University of Illinois Urbana-Champaign have demonstrated techniques for slowing light on photonic chips. Their findings, published in Nature Communications, enable high spectral resolution features on-chip and have utility for both classical and quantum photonics.
Photonic chips use optical cavities called resonators to manipulate light. The performance of these resonators is assessed by their Q, or quality factor: the longer light lives in a resonator, the higher its Q.
“One of the most efficient ways to store light is by slowing it down,” said Elizabeth Goldschmidt, an associate professor of physics and the senior author of the paper. “Slowing the propagation acts like storage: if you make a long path and slow it down, it lives there for a while.”
Extending this storage time is important for quantum memory, which relies on the ability to store light without destroying the quantum information contained within. Building quantum memory on-chip is important for deployability, manufacturability, and robustness. However, this is currently only possible using high-quality bulk optics, since intrinsic defects from manufacturing lead to light loss on chips.
To combat these defects, Goldschmidt and her colleagues explored a different light storage strategy: simply extending the propagation time. Using a technique known as spectral hole burning, the researchers were able to slow light on-chip by nearly one thousand times. Known as a slow-light effect, this phenomenon results from the propagation of light through a medium at a significantly reduced velocity. Goldschmidt’s lab is the first to investigate the slow-light effect on-chip.
“I was doing spectral hole burning in a resonator while trying to make more efficient quantum memories,” said Priyash Barya, a graduate student in the Department of Electrical and Computer Engineering and the paper’s lead author. “I was seeing an unexpected dip during our scan, which didn’t make sense. We eventually concluded that this dip was caused by the slow-light effect.”
To reproduce the slow-light effect, the research team turned to erbium-doped lithium niobate — an ideal medium because of its high density and coherence. The tunability of their platform over a large bandwidth adds an additional unique quality.
“Normally you make a device with the intention of doing one thing, and if you want to do something different, you have to make a new device,” Barya said. “But because we’re using spectral hole burning to give the device its properties, we can reconfigure as often as we want, over and over again.”
The Illinois Grainger Engineers believe their technique can eventually be used for a number of classical and quantum applications that currently rely on bulk optics.
“We think this platform can be used for all sorts of things, like quantum memory on-chip, slowing down single photons in order to store them, and making more exotic structures on-chip by doing things more complicated that just burning single spectral holes,” Goldschmidt said. “We’re a hammer looking for nails, and we’ve already found a lot.”
The study, ‘Ultra high-Q tunable microring resonators enabled by slow light,’ is available online. DOI: https://www.nature.com/articles/s41467-025-65533-1
Illinois Grainger Engineering Affiliations
Elizabeth Goldschmidt is an Illinois Grainger Engineering associate professor of physics in the Department of Physics. She is affiliated with the Materials Research Laboratory and is the Associate Director of the Illinois Quantum and Information Science and Technology Center.