A stealth bomber
Photo: Prayitno (Flickr)

Cutting-edge physics has driven military innovation for over a century, from Marie Curie’s x-ray machines of World War I to the quest for the atomic bomb during World War II. But these days, government defense departments are funding even more esoteric pursuits. We learned recently that the US Department of Defense is funding time crystals, and now Canada is funding a quantum radar system.

The University of Waterloo’s Institute for Quantum Computing announced today that it has received a $2.7 million investment from Canada’s Department of National Defence in order to develop quantum-based radar. Such a system is meant to scan the skies for stealth aircraft while overcoming a very Canadian problem: the aurora borealis, which causes static in traditional radar systems.

The project, which involves a bright light source to generate entangled photons, will have applications beyond just war.

“Having a good, bright, on-demand source of quantum photons would be useful for many things,” researcher Jonathan Baugh from the University of Waterloo told Gizmodo. Those applications include a few things you may have heard of, including quantum cryptography.

You might remember that entanglement is a spooky, strictly quantum phenomenon in which two subatomic particles share an innate connection. Essentially, you can’t describe one photon’s properties alone—they’re eerily connected by the same mathematical properties, no matter how far apart you separate them. If you measure one entangled particle, you can automatically assume something about the other.

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These entangled photons would serve as the source of a quantum radar. Normal radars shine radio-frequency light particles into the sky, and detect those that are reflected back from something flying overhead. With a quantum radar, you create two entangled light particles, keep one, and send its entangled partner into the sky. It either goes out into space or bounces off of your source (say, a spy plane) and back into your detector.

This might just sound like regular radar, but it relies on something called quantum illumination. Using entangled photons produces a far stronger signal than unentangled photons in the presence of lots of extra noise. In this case, the noise comes from the Arctic sky, where the aurora borealis sends electromagnetic energy at lots of different wavelengths, including visible light and radio waves, down to Earth. Scientists can spot entanglement by comparing measurements of light particles in the lab to those of the particles that bounce back into the detector.

Such a bright source would be useful for more than just the military, though. It could be used to set up an entangled link between computers in order to send quantum-secure messages, for example.

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These innovations, as usual, are not around the corner just yet. The North American Aerospace Defense Command (NORAD) Arctic radar stations will be in use until 2025 at least, according to the news release.  The researchers don’t yet have any quantum system they can actually beam into the sky.

But it’s the next example of an obvious theme with a long history: Governments will happily fund super-weird physics if there’s a potential military application.

[Phys.org]

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