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Saturday 6 October 2018

Antimatter seen in two places

මෙය 2018 සැප්තැම්බර් 15 නිව්සයන්ටිස්ට් සඟරාවේ පළ වූ ලිපියක්. ද්ඬිකෝටිකය ඇතැම් අවස්ථාවල ප්‍රමාණවත් නොවන බව මේ නිරීක්‍ෂණයෙන් ද පැහැදිළි වෙනවා. මා මෙහි දී යොදා ගන්නේ නිරීක්‍ෂණයක් මිස ප්‍රවාදයක් නොවෙයි.

Antimatter seen in two places at once thanks to quantum experiment

By Leah Crane

A PARTICLE can be in two places at once – even if it is made of antimatter. The result comes from an antimatter twist on a classic experiment to show a central tenet of quantum mechanics: that all particles are also waves.

In the basic double-slit experiment, a beam of light illuminates a plate with two parallel slits in it, creating stripes of light on a screen behind.

Thinking of light as single particles, as Isaac Newton argued, you would expect just two bright lines, corresponding to the two slits. Instead, you get an interference pattern of many stripes. This can be explained either as individual particles being in two places at once and interfering with themselves, or light behaving as a wave.

Variations of the experiment have been repeated with many types of particles, showing that they are all waves as well. However until now, it had never been done with a beam of antimatter.

“Antimatter is precious, it’s hard to produce, and it’s even harder to produce in a set-up where you can make a beam out of it,” says Michael Peskin at the SLAC National Accelerator Laboratory in California, who was not involved in the work.

Now, Akitaka Ariga at the University of Bern in Switzerland and his team have performed the double-slit experiment with positrons, the antimatter equivalent of electrons.

The set-up starts with radioactive sodium, which sheds about 5000 positrons per second. The positrons pass through a pair of circular openings, which focus them into a beam. This is then aimed at two silicon nitride crystals, each of which acts as a set of many slits. Positrons that pass through the crystals hit a screen that records where each one lands.

Only about 100 positrons per second hit the screen, so the experiment had to run for 200 hours to build up a strong image, revealing stripes of light and dark and showing that positron waves do interfere (

This isn’t the first time that antimatter particles have been shown to also behave like waves, says Peskin, but it is satisfying to achieve the classic double-slit. “It’s a big technical challenge.”

This experiment was a first step for the researchers’ ongoing efforts to study the effect of gravity on antimatter, such as whether it floats upwards. Their eventual goal is to determine how the interference pattern changes when the positrons are under a varying gravitational force.

“It’s possible that gravity doesn’t work exactly the same for antiparticles and particles, and this could be part of the reason the universe doesn’t appear to be made of the same amount of particles and antiparticles,” says David Christian at the Fermi National Accelerator Laboratory in Illinois.

If gravity does act differently on matter and antimatter, it is only a very slight distinction, so experiments will need to be extremely precise to reveal it.

“The effect of gravity on an individual particle is really tiny, even if it’s the gravity of the whole Earth,” says Christian.