Columbia Engineering researchers have taken another step toward shrinking quantum hardware.
The team has created an ultrathin metasurface device that boosts nonlinear optical effects at the nanoscale.
The advance builds on work published earlier this year, when the group showed that a crystalline device just 3.4 micrometers thick could generate entangled photon pairs.
The new study shows how the team cut that scale down to only 160 nanometers.
They achieved this by introducing metasurfaces. These structures rely on artificial patterns etched into ultrathin crystals to unlock optical behaviors not found in nature.
Corresponding author Chiara Trovatello said the group found a reliable approach to engineer these materials.
“We’ve established a successful recipe to pattern ultrathin crystals at the nanoscale to enhance nonlinearity while maintaining their sub-wavelength-thickness,” she said. Trovatello is now an assistant professor at Politecnico di Milano.
The Schuck lab works with transition metal dichalcogenides. These crystals can be peeled into layers only atoms thick.
Researchers stack them to create optical properties suited for quantum systems. But the layers remained too thin to generate photons efficiently. That limited the material’s usefulness.
Trovatello said quantum hardware demands compact components. She noted that current qubit sources occupy several centimeters and require large equipment rooms.
“To make quantum technologies scalable, we need to shrink the size of our qubit sources,” she said.
Earlier this year, the group used periodic poling to generate photons by arranging layers of molybdenum disulfide in alternating directions. That alignment ensured proper phase matching.
The new work takes a different route. PhD student Zhi Hao Peng etched repeating nanoscale lines into a molybdenum disulfide flake. The pattern created strong nonlinear effects beyond what traditional tuning could achieve.
“Our design enhances the nonlinear effects much more than traditional linear optical optimization techniques, and therefore achieves strong enhancement not previously possible,” Peng said.
The metasurface increased second harmonic generation by nearly 150 times relative to unpatterned samples. In that process, two photons merge into one with double the frequency.
The team now aims to reverse the conversion and split one photon into two entangled photons.
Peng’s method also reduces fabrication complexity. Jim Schuck, the senior investigator, highlighted that benefit.
“Nonlinear crystals have been key to a lot of photonic technologies, but these materials can be brittle and have been notoriously difficult to shape and fabricate,” he said.
He added that Peng created a simple approach that works with standard cleanroom tools.
Toward on-chip quantum systems
Theoretical collaborators helped identify the best pattern for large nonlinear responses. Michele Cortufo said the structure relied on alternating line widths to achieve “nontrivial behavior” in flakes this thin.
Andrea Alu noted that the work shows how engineered nonlocalities in metasurfaces can enable “compact, integrable platforms” for nonlinear optics.
The device operates at telecom wavelengths, which makes future integration easier. Schuck said the footprint points toward fully on-chip quantum photonics.
The study is published in the journal Nature Photonics.