Scaling quantum computers requires more than adding qubits; it depends on maintaining precise control over their physical environment. One persistent challenge is cooling. Trapped-ion quantum systems must be cooled to extremely low temperatures to reduce motion that interferes with quantum operations. While integrated photonic chips promise scalable architectures, they have so far struggled to match the cooling performance achieved with large, external optical systems.
Clements, E., Knollmann, F. W., Corsetti, S., Li, Z., Hattori, A., Notaros, M., Swint, R., Sneh, T., Kim, M. E., Leu, A. D., Callahan, P., Mahony, T., West, G. N., Sorace-Agaskar, C., Kharas, D., McConnell, R., Bruzewicz, C. D., Chuang, I. L., Notaros, J., & Chiaverini, J. (2026). Sub-Doppler Cooling of a Trapped Ion in a Phase-Stable Polarization Gradient. Physical Review Letters, 136(2), 023201. https://doi.org/10.1103/fy3t-f1hz
Jelena Notaros at the Massachusetts Institute of Technology and MIT Lincoln Laboratory proposes a solution that brings advanced cooling techniques directly onto a photonic chip. The team demonstrated a compact, energy-efficient method that cools trapped ions well below the standard laser-cooling limit, using precisely engineered on-chip photonic structures rather than bulky external optics.
Jelena Notaros at the Massachusetts Institute of Technology and MIT Lincoln Laboratory stated,
“We were able to design polarization-diverse integrated-photonics devices, utilize them to develop a variety of novel integrated-photonics-based systems, and apply them to show very efficient ion cooling. However, this is just the beginning of what we can do using these devices. By introducing polarization diversity to integrated-photonics-based trapped-ion systems, this work opens the door to a variety of advanced operations for trapped ions that weren’t previously attainable, even beyond efficient ion cooling—all research directions we are excited to explore in the future.”
The approach centers on an integrated photonic chip designed with nanoscale optical antennas and waveguides that generate tightly controlled light fields. These fields interact with ions trapped just above the chip surface. By carefully shaping the polarization and intersection of multiple light beams, the researchers implemented polarization-gradient cooling, a technique known to extract more vibrational energy from ions than conventional laser cooling.
In traditional trapped-ion systems, polarization-gradient cooling requires a complex arrangement of external mirrors, lenses, and beam splitters. These components occupy significant space and are sensitive to vibration and alignment drift. In contrast, the integrated design routes light through stable waveguides etched directly into the chip, allowing the optical patterns needed for cooling to remain phase-stable over time.
The photonic chip incorporates pairs of nanoscale antennas that emit intersecting beams with different polarizations. Where these beams overlap, they create rotating light fields that exert forces on the ion, damping its motion more efficiently than single-beam approaches. The antennas are patterned with carefully spaced features that direct light upward toward the ion while maximizing optical efficiency.
Using this architecture, the researchers achieved cooling nearly an order of magnitude below the Doppler limit, a benchmark that defines the lowest temperature reachable with standard laser cooling alone. Importantly, the system reached these temperatures in roughly 100 microseconds, significantly faster than many existing methods. Faster cooling reduces idle time between quantum operations and improves overall system stability.
The work focuses on trapped-ion qubits, where information is encoded in the internal states of charged atoms confined by electromagnetic fields. Trapped ions are attractive qubits because they exhibit long coherence times and high-fidelity operations. However, scaling these systems to large numbers of ions has been difficult due to the size and complexity of the required optical infrastructure. Integrated photonics offers a path toward placing thousands of ion-control sites on a single chip, provided performance limitations such as cooling can be overcome.
Beyond demonstrating improved cooling, the study highlights broader advantages of integrated photonic control. Light emitted from on-chip antennas shows reduced sensitivity to external vibrations and environmental fluctuations compared to free-space optics. This stability enables more consistent quantum-state preparation and opens opportunities for additional on-chip operations beyond cooling, including state manipulation and entanglement protocols.
Looking ahead, the team plans to extend the approach to systems involving multiple ions and to explore alternative chip architectures that further integrate optical control elements. If successful, these efforts could reduce the size, power consumption, and complexity of trapped-ion quantum computers, bringing chip-based quantum processors closer to practical deployment.
Rather than relying on increasingly elaborate external systems, the work illustrates a shift toward embedding critical quantum functions directly into hardware. By integrating efficient cooling into photonic chips, the researchers address a foundational obstacle to scalable quantum computing and provide a framework that could be adapted to other quantum platforms requiring precise thermal and optical control.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
