Insider Brief
- University of Illinois researchers developed an on-chip quantum memory that stored photons for more than 1 microsecond while preserving quantum information with high fidelity.
- The device uses erbium atoms in thin-film lithium niobate to temporarily hold multiple photons, offering potential compatibility with large-scale chip manufacturing.
- Practical use in quantum computers and communication networks will require improved photon retrieval efficiency and longer storage times.
- Image: Pictured left to right: Priyash Barya, Daren Chen, Elizabeth Goldschmidt. (University of Illinois Urbana-Champaign)
PRESS RELEASE — For highly fragile quantum information systems, the ability to store quantum information is vital — but also challenging. Quantum information is transported in particles of light called photons, which often must be temporarily paused (or “stored”) while other, slower quantum operations catch up. This storage must be performed on microchips as small as one centimeter — a distance covered by light in a few trillionths of a second. Storing photons for a microsecond would represent a massive leap forward for the capabilities of quantum chips.
New research from The Grainger College of Engineering at the University of Illinois Urbana-Champaign addresses this challenge by developing an integrated on-chip nanophotonic platform for longer-term storage of photons. Led by physics professor Elizabeth Goldschmidt and published in Nano Letters , the group’s integrated platform leverages the versatility of spectral hole burning and the scalability of thin-film lithium niobate, giving it potential for scalable manufacturing, with implications for both classical and quantum photonics.
“No one else has stored light on a chip in a platform like this, with this potential for scalability,” said Priyash Barya, an electrical engineering graduate student and the paper’s co-first author. “Our technique is the only way of doing this, and we’re doing it on one of the leading platforms for quantum optics and quantum information systems. It’s a futuristic platform with industry scalability.”
There are two broad ways to store photons. Using conventional photonics, a field that utilizes macroscopic components like optical fibers and mirrors, scientists can delay light by extending its travel path — but this comes at a cost. Photons are easily absorbed by matter, and traveling for longer distances increases the likelihood of absorption. A photon is unlikely to survive the distances required for quantum-relevant delays, making conventional photonic storage highly inefficient. Alternatively, photons can be coupled to highly coherent atoms for longer storage. However, integrating such atoms with scalable nanophotonic platforms is largely out of reach.
“Long delays are an outstanding problem in quantum information processing,” said Daren Chen, a physics graduate student and the paper’s co-first author. “We wanted to demonstrate a very promising approach for this using our nanophotonic platform.”
Members of Goldschmidt’s lab tackled the problem by building on previous work in rare earth-doped materials systems and spectral hole burning-induced slow light . The Illinois researchers fabricated a nanoscale waveguide made of thin-film lithium niobate (TFLN), a material known for its strong light confinement, low optical loss and wafer-scale integration, and doped with erbium atoms, which have desirable quantum properties. A tunable laser was used to spectrally arrange the atoms into a comb-like pattern with even spacing between each frequency peak. Known as an atomic frequency comb, this design enables the atoms to temporarily “catch” and “hold” incoming photons for a predetermined amount of time.
The resulting device demonstrated high-fidelity preservation of quantum information, with storage times exceeding 1 microsecond and the ability to store multiple photons at once. Most importantly, it has the potential for commercial scalability and is easy to replicate.
“This is not a one-off bespoke device,” Goldschmidt said. “Its promise is in its simplicity: we’ve taken something that can typically only be done in a highly specialized laboratory environment and recast it in a platform that can be made commercially at scale by people who don’t know anything about quantum optics.”
Goldschmidt sees the pioneering platform as a step toward integrating quantum memories into scalable, chip-based quantum computers and communication networks. A practical version of the device will need to demonstrate better retrieval efficiency and longer storage times — efforts the group will pursue by improving their frequency comb and experimenting with different erbium isotopes that are more impervious to noise. Goldschmidt’s lab is also exploring additional applications for their technique.
“This project is one component in the set of things we’re working on,” Goldschmidt said. “We’re building up capabilities in this particular integrated photonics platform, and we have lots of other plans for using this technique of spectrally tailoring the ensemble to build other devices for quantum photonics.”