In the suburbs of Chicago, about 34 miles west of Lake Michigan, lies a hole in the ground that drops some 330 feet below. Long ago, scientists had drilled the well for a particle physics experiment that long since disappeared from this world. Now, in a few years, they will be reusing the shaft for a new project with the name Mystic. MAGIS-100.
When MAGIS-100 is complete, physicists plan to use it to detect hidden treasures: dark matter, the mysterious invisible something that is believed to make up much of the universe; and gravitational waves, ripples in space-time caused by cosmic shocks like black hole collisions. They hope to find traces of these elusive phenomena by observing the quantum signatures they leave behind raindrop-sized clouds of strontium atoms.
But actually looking at those atoms is more complicated than you might expect. To carry out similar experiments, physicists have so far relied on cameras comparable to those in a smartphone. And while the technology might work well for a sunset or a tasty meal, it limits what physicists can see at the atomic level.
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Fortunately, some physicists may have an upgrade. A research team from different groups in Stanford, California, has created a unique camera contraption which is supported by a dome of mirrors. The extra reflections help them see what light is entering the lens and what angle a particular patch of light is coming from. That, they hope, will allow them to peer into an atomic cloud like never before.
Your cell phone or DSLR camera doesn’t care where the light travels from: it captures the intensity of photons and colors reflected by wavelengths, little else. For taking pictures of your family, a city skyline, or the Grand Canyon, that’s fine. But for studying atoms, it leaves a lot to be desired. “You’re wasting a lot of light,” he says Murtaza Safdarigraduate student in physics at Stanford University and one of the creators.
Physicists want to preserve that information because it allows them to paint a more complex 3D picture of the object (or objects) they are studying. And when it comes to the meticulous analyzes that physicists like to do, the more information they can get at once, the faster and the better.
One way to get that information is to set up multiple cameras, allowing them to take pictures from multiple angles and stitch them together for a more detailed view. That can work very well with, say, five cameras. But some physics experiments require measurements so precise that even a thousand cameras might not work.
So, in a Stanford basement, the researchers decided to set out to create their own system to solve that problem. “Our thought…was basically: Can we try to fully capture as much information as we can, and can we preserve directional information?” Safdari says.
His resulting prototype, made from off-the-shelf and 3D-printed components, looks like a shallow dome, adorned with a series of tiny mirror-like dots on the inside. The pattern appears to form a fun optical illusion of concentric circles, but it’s carefully calculated to maximize the light hitting the camera.
For the MAGIS-100 project, the subject of the shot, the cloud of strontium atoms, would be inside the dome. A brief flash of light from an external laser beam would scatter past the mirror points and through the cloud at a myriad of angles. The lens would capture the resulting reflections, how they have interacted with the molecules, and from which points they have bounced.
Then, from that information, machine learning algorithms can reconstruct the three-dimensional structure of the cloud. Currently, this reconstruction takes many seconds; in an ideal world, it would take milliseconds, or even less. But, like the algorithms used to train self-driving cars to adapt to the world around them, the researchers believe the performance of their computer codes will improve.
While the creators haven’t tested the camera on atoms yet, they did test it by scanning a few suitably sized sample parts: 3D-printed letter-shaped parts the size of the strontium droplets they intended to use. The photo they took was so clear that they were able to find flaws where the small letters D, O and E differed from their intended design.
For atomic experiments like MAGIS-100, this equipment is unlike any other on the market. “The state of the art is just cameras, commercial cameras and lenses,” he says Ariel Schwartzman, a physicist at the SLAC National Accelerator Laboratory in California and co-creator of the Stanford configuration. They scoured photographic equipment catalogs for something that could see an atomic cloud from multiple angles at once. “There was nothing available,” says Schwartzman.
To complicate matters, many experiments require atoms to rest in extremely cold temperatures, just above absolute zero. This means they require low light conditions – shining any bright light source on them for too long could heat them up too quickly. adjustment longer exposure time in a camera it might help, but it also means sacrificing some of the details and information needed in the final image. “You are allowing the cloud of atoms to diffuse,” he says. Sanha Cheong, a graduate student in physics at Stanford University and a member of the chamber construction team. The mirror dome, on the other hand, aims to use only a short laser flash with a microsecond exposure.
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The next challenge for the creators is to position the camera on MAGIS-100, which will require a lot of adjustment to position the camera on a much larger axis and in a vacuum. But physicists are hopeful: a camera like this could go far beyond detecting dark effects around atoms. Its designers plan to use it for everything from tracking particles in plasma to measuring quality control of small parts in the factory.
“Being able to capture the most light and information in a single shot with the shortest possible exposure opens up new doors,” says Cheong.