Led by Jim Schuck, professor of mechanical engineering at Columbia Engineering, and detailed in an October publication in Nature Photonics, a new method successfully shrinks nonlinear optical platforms down to 160 nanometers while maintaining high efficiency. The Columbia Engineers achieved this by introducing metasurfaces—artificial geometries etched into ultrathin transition metal dichalcogenides (TMDs)—to imbue the crystals with enhanced optical properties. This innovation addresses a critical need for scalable quantum technologies, as current qubit sources occupy substantial space; the team’s design enhances second-harmonic generation by almost 150 times compared to unpatterned samples.
Enhancing Nonlinear Optical Properties with Metasurfaces
Researchers have successfully enhanced nonlinear optical properties by integrating metasurfaces with ultrathin crystals, specifically transition metal dichalcogenides (TMDs). These metasurfaces, created by etching nanoscale patterns onto the crystals, imbue them with new optical characteristics. The team achieved a significant boost – nearly 150 times greater – in second-harmonic generation compared to unpatterned samples. This process merges two photons into one with double the frequency, a critical step towards scalable quantum technologies requiring compact light sources.
The innovation lies in a deceptively simple nanofabrication technique developed by PhD student Zhi Hao Peng. This method allows for the creation of patterned lines on molybdenum disulfide flakes, enhancing nonlinear effects beyond traditional optimization methods. Importantly, this approach is easier and cheaper to execute than previous patterning techniques, addressing a long-standing challenge in fabricating nonlinear crystals, which can be brittle and difficult to shape.
This advancement paves the way for “on-chip quantum photonics,” as the metasurface design operates at the nanoscale and produces light at telecommunications wavelengths. Theoretical collaborators determined the optimal metasurface pattern for boosting nonlinear response, and the resulting device is one of the first to effectively combine metasurfaces with 2D crystals. The team is now focused on reversing the process – splitting one photon into two entangled ones – leveraging this enhanced efficiency.
TMD Crystals and Their Unique Characteristics
Researchers have developed a technique to enhance nonlinear optical properties in transition metal dichalcogenides (TMDs), crystalline materials that can be reduced to atom-thin layers. By introducing metasurfaces—artificial geometries etched into these ultrathin crystals—they’ve created platforms with boosted functionality. This approach allows for customization and control of optical properties at the nanoscale, overcoming limitations previously seen in conventional nonlinear crystals. The resulting devices are only 160 nanometers thick, crucial for scaling quantum technologies.
A key finding detailed in Nature Photonics is the significant enhancement of second-harmonic generation—where two photons merge into one with double the frequency—achieved through this metasurface design. Specifically, the team observed a nearly 150-fold increase compared to unpatterned samples. This enhancement is due to a patterned arrangement of lines etched onto a molybdenum disulfide flake, effectively boosting nonlinear effects beyond traditional optimization techniques. This optimized process paves the way for splitting photons into entangled pairs.
The fabrication technique developed by Peng is notably simple and cost-effective, requiring fewer steps than previous patterning methods. This simplicity, combined with the potential for integration with current telecommunications networks at a nanometer scale, positions these TMD metasurfaces as promising components for fully on-chip quantum photonics. The resulting devices are extremely small – just 3.4 micrometers thick – and offer a path toward scalable quantum technologies that currently occupy entire rooms.
Our design enhances the nonlinear effects much more than traditional linear optical optimization techniques, and therefore achieves strong enhancement not previously possible.
Zhi Hao Peng
Techniques for Generating and Manipulating Photons
Researchers have developed a technique to enhance nonlinear optical properties in ultrathin crystals, specifically transition metal dichalcogenides (TMDs), down to 160 nanometers using metasurfaces. These metasurfaces, created by etching nanoscale patterns into the crystals, imbue them with new optical properties. This approach allows for enhanced nonlinearity while maintaining the crystals’ sub-wavelength thickness—critical for applications needing minimized size, like quantum technologies, where current qubit sources occupy entire rooms.
The team achieved a nearly 150-fold enhancement in second-harmonic generation—a process where two photons merge into one with double the frequency—by etching repeating lines onto a molybdenum disulfide flake. This surpasses traditional linear optical optimization techniques. Notably, the nanofabrication technique developed by PhD student Zhi Hao Peng is simpler and cheaper than prior patterning methods, addressing the historical difficulty in shaping brittle nonlinear crystals.
Theoretical collaborators determined a specific metasurface pattern—a periodic arrangement of lines with alternating widths—to maximize the nonlinear response of the TMDs. This work combines metasurfaces with 2D crystals to achieve potent effects, generating telecommunications-range wavelengths which facilitates integration with existing networks. The resulting compact source of entangled photons could pave the way for fully on-chip quantum photonics.
Scaling Quantum Technologies with Nanoscale Devices
Researchers have successfully shrunk nonlinear optical platforms down to 160 nanometers by introducing metasurfaces onto ultrathin crystals. These metasurfaces, created by etching patterns into transition metal dichalcogenides (TMDs) like molybdenum disulfide, enhance nonlinearity while maintaining sub-wavelength thickness. This achievement is crucial for scaling quantum technologies, as current qubit sources occupy significant space – even entire rooms – and smaller footprints are needed for practical quantum processors.
The team’s design enhanced second-harmonic generation – where two photons merge into one with double the frequency – by almost 150 times compared to unpatterned samples. This was achieved through a deceptively simple nanofabrication technique involving etching repeating lines onto a TMD flake. This approach is notable because it requires fewer steps and is cheaper to execute than previous patterning methods, potentially paving the way for more complex and integrable quantum photonic devices.
This work enables the possibility of “fully on-chip quantum photonics” by producing light at telecommunications-range wavelengths. The resulting devices are significantly more compact than existing sources of entangled photons, offering a pathway towards scalable quantum technologies. Theoretical collaborators confirmed that patterning flat flakes with lines of alternating widths unlocked unprecedented nonlinear efficiencies when combined with 2D materials like TMDs.
