• Physics 18, 151
A 10-µm-wide microchip can generate light with any desired direction, polarization, and intensity, which will be handy for future quantum technologies.
Emerging technologies for quantum computing and cryptography require small components capable of emitting photons whose properties are precisely controlled. Researchers have been developing such components, and now a team has demonstrated a technique that provides control of direction, polarization, and intensity simultaneously [1]. Like previous experiments, the technique uses microscopic structures on a semiconductor surface to convert wave-like surface excitations to light waves. But the new demonstration uses shapes for these structures that allow more precise control over the outgoing light. The team expects the new technique to find wide use in efforts to build quantum technologies in miniature solid-state devices.
Solid-state miniaturization is one of the few realistic routes toward making quantum technologies practical, scalable, and easily manufacturable, says Fei Ding of the University of Southern Denmark. But there are not many good compact photon sources. “The technology really requires a compact and flexible solid-state photon source that gives us full control over how light is emitted—its direction, polarization, and spatial profile,” Ding says. “This is crucial for building scalable quantum and nanophotonic technologies, where single photons are used as the fundamental carriers of information.”
To work toward this capability, Ding and colleagues sought to extend previous research exploring the generation of photons using a so-called “metasurface”—a layer of patterned material deposited on a semiconducting chip. Researchers place a nanoscale, photon-emitting object called a quantum emitter on this surface and hit it with a laser pulse. In response, the emitter generates surface plasmon polaritons—excitations involving both electromagnetic waves and charge motion. As the polaritons travel through the metasurface pattern of scattering objects, energy leaks out to produce photons traveling in free space.
Using this approach, researchers have not yet managed to simultaneously control photon direction, polarization, and intensity, or to produce multiple photon beams pointing in different directions and having different polarizations. Ding and colleagues have now shown how to overcome these challenges.
They built their device on a 30-nm-thick wafer of silicon dioxide resting on a 150-nm-thick silver mirror as a base. For their quantum emitter, the researchers used a nanometer-scale diamond containing some nitrogen atoms paired with carbon vacancies. The polariton waves produced by the laser pulse spread out from the diamond, passing through a region in which the team laid down a pattern of many 35-nm-thick strips of silver, 200 nm apart. These objects act like antennae and reradiate the energy of the polariton waves outward into free space.
Importantly, these strips are rectangles, a less symmetric shape than the elements used in previous experiments. The anisotropy of this shape allowed the researchers to independently control the phases of the two polarization components—left and right circular polarization—of the emitted photons. This independent control let them choose the properties of outgoing photons with precision, including the light waves’ spatial profile. Ding and colleagues demonstrated the production of both linearly and circularly polarized light emitted in a chosen direction as well as emission in multiple directions at once. “What’s new here is that we can now generate single or multiple beams with arbitrary direction, polarization, and intensity ratios, all from one general design framework,” Ding says.
“The work holds promise for many opportunities in the generation and management of light,” says Andrea Alù, a photonics expert from the City University of New York. “It builds on previous work,” he says, “but now they integrate optical sources in the form of single-photon quantum emitters, shaping light emission with flexibility.”
In future work, Ding and colleagues hope to integrate this photon emission platform into a system with electrically driven quantum emitters—rather than relying on laser excitation—which would be easier to integrate into a commercial microchip circuit.
–Mark Buchanan
Mark Buchanan is a freelance science writer who splits his time between Abergavenny, UK, and Notre Dame de Courson, France.
References
- S. Sande et al., “On-chip emitter-coupled meta-optics for versatile photon sources,” Phys. Rev. Lett. 135, 086902 (2025).
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