Driverless cars can use pulses of laser light to sense objects and measure how far away they are, but this can fail when it is very bright out or a lot of light is reflected from nearby vehicles. Swapping out the lasers for particles of quantum light could make it easier for autonomous vehicles to avoid collisions.
Lidar uses laser light to detect objects, similar to how radar uses radio waves. But there are a lot of sources of light on a road, which can interfere with this detection.
鈥淚f you want to detect an object in the direction of the sun, you have such a problem. The background is so bright that the signal is buried in the noise,鈥� says at Zhejiang University in China.
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In conventional lidar sensors, lasers emit pulses of light that bounce off objects and into a detector. The time it takes the reflected light to reach the detector depends on how far away the object is, and this data can be converted into a map.
Wang and his colleagues took advantage of quantum effects to make lidar more immune to errors. The researchers passed laser light through a special crystal to create two photons, or particles of light, that were entangled. This meant that changing the quantum properties of one photon changed the properties of the other.
The two photons then entered a maze of mirrors and lenses, which directed one of them, called a probe photon, to leave the device and bounce off any objects it encountered, while the other, called a reference photon, travelled to the detector.
Thanks to entanglement, information about the probe photon鈥檚 collisions with objects could be obtained by measuring the properties of the reference photon. Because photons don鈥檛 have mass or charge, they only interact with each other under extreme circumstances, so the probe photon鈥檚 state was not changed by the photons of ambient light.
This quantum-enhanced lidar was much more resilient to light interference than the traditional lidar. The researchers tried to fool it by illuminating the target object with LED light 10 times stronger than the stream of probe photons that the device repeatedly emitted. But it worked as usual, says Wang. Then they 鈥渁ttacked鈥� the device with a laser 10,000 times stronger, and only a small part of the lidar鈥檚 output became unusable, he says.
at the University of Pavia in Italy says his is not the first experiment to use photons and quantum effects in lidar, but it deals with the issue of unwanted ambient light unprecedentedly well. The quantum approach also has the benefit of being able to detect objects that are not very reflective using less light and less power than conventional lidar, he says.
However, the team鈥檚 device is still largely proof-of-principle and will have to be shrunk down and integrated onto chips before it can be used outside of the lab.
Journal reference:
Physical Review Letters,
