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The control of light by a newly developed system of nanoantennas could have important applications in fields as diverse as quantum computing and medicine.
As far as we know, there is nothing faster than light traveling through a vacuum, and photons travel through materials pretty quickly too. This has a consequence; it means that photons have a vastly reduced chance of interacting with atoms and molecules as they pass through a medium. This may not seem like much of a problem, but for the designers of quantum computers and other forms of technology that use light to transmit information, it can severely reduce efficiency.
If only there were some way to impede the progress of photons, even perhaps steer them in the desired direction. Such a development would provide a significant boost for applications that use light to store and transmit information.
Researchers from Stanford University, California, think they may have made such a breakthrough. In a paper published this month in the journal Nature Nanotechnology, the team of scientists from the lab of Jennifer Dionne, associate professor of materials science and engineering, detail an approach to significantly slow and direct light.
The method developed by the researchers functions almost like an echo-chamber, but for light rather than sound. The technology relies on ultrathin silicon chips structured into nanoscale bars, which the team call high-quality-factor (high-Q) resonators.
The researchers describe the technology as essentially a way to ‘trap light in a tiny box’ — photons are allowed to enter from many directions, but the way they leave is controlled. These bars can ‘trap’ light and then release or even redirect it.
The high-Q resonators demonstrated a resonance behavior proportional to the lifetime of the light that is 100 times greater than any previous similar devices. This quantity (up to 2500), described by the researchers as the ‘sweet spot’ for such tech, leads to novel light manipulation techniques and applications in fields as diverse as quantum computing, light-based wi-fi, virtual reality, and even the detection of viruses such as SARS-CoV2.
Drawing a Trap for Light
Building a nanoscale trap for light is no small challenge, and many silicon-based devices cannot trap light as elements are transparent. This means constructing an exceptional silicon-based device.
The central component of this device is a thin layer of silicon placed on top of a wafer of sapphire. Silicon is the material of choice here because it traps light and has low absorption in the near-infrared part of the electromagnetic spectrum.
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The researchers then painstakingly carve a nanoantenna pattern into this wafer using an electron microscope. This antenna pattern, which has to be ‘drawn’ extremely smoothly, acts as the ‘walls’ to this photon echo-chamber, and that means that any imperfections in these walls would scatter light and severely reduce the ability of high-Q to pen in light.
The design used to create the high-Q nanostructures had to be very carefully chosen, while they needed to find a pattern with a decent enough photon-penning efficiency within the remit of current fabrication methods. Playing around with the design led the team to a platform with multiple practical applications , including tackling a growing crisis.
Controlling Light Could Curb COVID-19
Detecting individual biomarkers is a particular application of high-Q nanoantennas. Biomarkers are tiny molecules that are essentially invisible. However, when light is passed over these molecules, eventually it is scattered. This could take hundreds or even thousands of passages, but it can still form the basis of a robust biomarker detection scheme — biosensing.
Researchers based in Jennifer Dionne’s lab, who is an associate professor of materials science and engineering at Stanford, are currently working with high-Q technology to help in the fight against COVID-19.
Dionne and her team believe that high-Q can be used to detect COVID-19 antigens and antibodies. The nano-resonators mean that the antenna can independently focus on different antibodies at the same time.
Global crises aside, perhaps the most critical application of the high-Q nanoantenna system is in the development of quantum computers. The technology could help physicists create entangled photons more efficiently.
Entanglement — of vital importance in quantum computers — is essentially when a change in one particle instantaneously changes the qualities of its entangled partner(s). The fact that even if these particles are at other ends of the Universe, this effect is instant, is deeply counter-intuitive, and troubled Einstein so much he labeled it “spooky action at a distance.”
Creating entangled particles currently requires optical experiments with huge and highly expensive polished crystals. The Stanford team says that by controlling and shaping entangled photons, the use of their nanostructures could help scale down entanglement generators to something that could fit in the palm of scientists’ hands.
This means they could also be used in a much smaller quantum computer, something that companies such as IBM and Google, currently jostling for so-called quantum supremacy, will likely be very interested in.
References and Further Reading
Lawerence. M, Barton. D. R, Dixon. J, Dionne. J. A. (2020) High-quality factor phase gradient metasurfaces. Nature Nanotechnology. https://doi.org/10.1038/s41565-020-0754-x