Columbia Engineers Develop Nanoscale Metasurfaces for Quantum Tech

Columbia University researchers have achieved a significant breakthrough in quantum technology by developing nanoscale metasurfaces that enhance nonlinear optical effects. This advancement, detailed in a paper published in *Nature Photonics* in October, enables the creation of efficient nonlinear platforms down to just 160 nanometers in thickness.

Led by Jim Schuck, a professor of mechanical engineering at Columbia Engineering, the team has focused on transition metal dichalcogenides (TMDs), a class of crystals that can be exfoliated to ultra-thin layers. Their innovative approach uses metasurfaces—artificial geometries etched into these crystals—to improve their optical properties significantly.

Transforming Quantum Technology

In January, the research team, including Chiara Trovatello, who is now an assistant professor at Politecnico di Milano, previously demonstrated a method for generating entangled photon pairs using a crystalline device only 3.4 micrometers thick. Trovatello explained the importance of size in quantum technologies, stating, “To make quantum technologies scalable, we need to shrink the size of our qubit sources.”

The challenge with traditional nonlinear crystals, such as those used in laser pointers, lies in their size. Current qubit sources occupy several centimeters, making them impractical for compact applications. The new nanoscale platforms aim to address this issue, offering a potential solution for more efficient quantum processors.

The team’s earlier work involved using a technique called periodic poling to enhance photon generation. By layering a TMD like molybdenum disulfide in alternating orientations, the layers were optimized for light wave phase-matching. The current study builds on this foundation by introducing a complementary platform with highly tunable, etched metasurfaces.

Innovative Metasurfaces and Their Impact

The research team, including Ph.D. student Zhi Hao Peng, developed a nanofabrication technique that etches repeating lines onto molybdenum disulfide. This design significantly enhances nonlinear effects, achieving an impressive 150-fold increase in second-harmonic generation compared to unpatterned samples. In this process, two photons combine to form a new photon with double the frequency and half the wavelength of the original particles.

Notably, Peng’s technique simplifies the fabrication process, allowing for more complex patterns with fewer steps and lower costs. “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,” Schuck remarked. “Peng figured out a technique that is deceptively simple.”

Theoretical collaborators Andrea Alu and Michele Cortufo from the CUNY Advanced Science Research Center contributed to determining the optimal metasurface pattern, demonstrating that simple modifications can lead to significant improvements. “This work demonstrates how engineered nonlocalities in metasurfaces can unlock unprecedented nonlinear efficiencies when combined with 2D materials,” Alu stated.

The development of these metasurfaces represents a significant step toward achieving compact, integrable platforms for nonlinear optics and light generation. The photons produced are compatible with telecommunications-range wavelengths, facilitating integration with existing networks.

“This could be one of the most compact sources of entangled photons at that wavelength range,” Schuck concluded. “With our footprint, we can really start to think about fully on-chip quantum photonics.”

As research continues, the implications of these findings could lead to more advanced quantum technologies, paving the way for more efficient and scalable quantum computing solutions.