Science & Technology

Replicating the double-slit experiment with anti-matter

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The Double-slit experiment is one of the most repeated experiments in the whole of physics, it first introduced scientists to the idea that a particle can have properties of both a particle and a wave. Now researchers, inspired by the work of Richard Feynman, have replicated the experiment with antimatter in order to ascertain if one of nature’s greatest surprises can be found in anti-particles too.

The ultimate aim, to discover if gravity has the same effect on antimatter as it does on matter. 

Although first applied to photons, the double slit experiment was later applied to electrons and then eventually, much larger particles of matter, all of which have displayed particle-wave duality. Even though wave behaviour has been demonstrated in antimatter before, this is the first that a full version of the double-slit experiment has been performed with positrons, the antimatter equivalent of electrons.

Part of the reason the experiment had never been performed in this way before is the associated difficulty of producing antimatter.

If you need to familiarise yourself with the double-slit experiment and its findings before continuing you can do so here.

Researchers, led by Akitaka Ariga from the University of Bern Switzerland, took advantage of the variable energy positron beam facility of the L-NESS lab in Como Italy.

The Positrons were sent through a system known as Talbot-Lau interferometer to a set-up equivalent to the apparatus used in the standard Double-slit experiment.

The Talbot-Lau set-up leading to a system analogous to that used to perform the standard double-slit experiment (Scampoli, Sala, Pistillo)

The Talbot-Lau set-up leading to a system analogous to that used to perform the standard double-slit experiment (Ariga)

The positrons were initially created by beta-decay in a radioactive sodium isotope embedded in a fine tungsten film. The slowly released positrons received a ‘kick’ of energy by use of an electrostatic system and were then focused into a continuous beam by circular collimators.

This beam was directed at silicon nitrate crystals acting as a diffraction grating. Positrons that passed through this makeshift diffraction grating impacted on an emulsion detector which recorded their position.

The experiment was left to run for 200 hours in order to build an acceptable interference pattern of light and dark bands as seen in the more conventional double-slit experiment.

Researchers found interference patterns in keeping what that of traditional matter, indicating that antimatter also possesses wave and particle-like attributes.

results from the two variations of the double-slit experiment

results from the two variations of the double-slit experiment

So what does this mean for the future study of antimatter?

The study was the first of a series intended to ascertain the effects of gravity on antimatter. Namely, will antimatter float upwards under the influence of gravity?

Further experiments will aim to measure how the interference demonstrated in this experiment alters when the positrons are introduced to a varying gravitational force. David Christian from Fermilab, Illinois,  suspects that gravity may work differently for matter and antimatter. This could be one of the reasons why the universe is populated with an abundance of matter rather than antimatter.

If gravity does have a different effect on antiparticles, then the difference in effect will be minuscule due to the almost insignificant effect of gravity on individual particles, thus requiring incredibly sensitive and precise measurement.

Original research available here.

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