Harvard researchers develop microscopic mirrors for quantum networks - Open Access Government
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Open Access NewsResearch & Innovation A fabricated micromirror array next to a penny, compared with a half-inch diameter commercial mirror. Credit© Brandon Grinkemeyer / Lukin lab at Harvard Harvard engineers have developed a method to create microscopic, ultra-smooth mirrors by inducing material stress that buckles thin coatings into shape. These high-performance components are essential for trapping light in future quantum networks Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have pioneered a new fabrication method to create ultra-smooth, microscopic mirrors. These mirrors form high-performance optical resonators, which are critical components for controlling single particles of light. The study, published in the journal Optica, provides a scalable solution for building the infrastructure of future quantum computers and long-distance quantum networks. Quantum networks: Harnessing material stress for precision Traditional microfabrication techniques often struggle to produce the surface smoothness required for advanced quantum applications. Standard etching and lithography can leave behind microscopic roughness that scatters light and reduces efficiency. To overcome this, the Harvard team utilised the natural mechanical properties of silicon and dielectric coatings. The process begins by growing a layer of silicon oxide on a silicon wafer to flatten any surface imperfections. After removing the oxide, the researchers deposit a stack of transparent layers known as a dielectric mirror coating. When a hole is etched through the back of the wafer to free the coating, the built-in mechanical stress causes the material to buckle into a perfectly curved, high-quality mirror. This “buckling” technique allows for precise control over the mirror’s curvature and the specific wavelengths of light it reflects. Achieving record-breaking performance The effectiveness of an optical resonator is often measured by its “finesse,” which indicates how many times light can bounce between mirrors before scattering.
The team demonstrated that their resonators could reach a finesse of 0.9 million at a wavelength of 780 nanometers. This means a photon can reflect back and forth nearly a million times within the cavity. This level of performance is vital for quantum networking, where single atoms must interact strongly with single photons. These cavities act as the interface that converts an atom’s quantum state into light for transmission through optical fibres. Beyond quantum computing While the primary motivation for the research was to support quantum networking, the scalability of this method suggests broader applications. The ability to build high-quality optical resonators directly onto chips could lead to advancements in integrated lasers, environmental sensing equipment, and ultra-compact spectroscopic sensors. By working with the inherent properties of the materials rather than fighting against fabrication limits, the team has created a robust path forward for integrated photonics.