Feynman’s double slit thought experiment come true

Scientists demonstrate the full realization of famous Feynman’s double slit thought experiment.

In “Feynman Lecture on Physics vol.3”, published in 1965, Richard Feynman outlined in a brilliant way (of course) the particle – wave duality of electrons.

We choose to examine a phenomenon which has in it the heart of quantum mechanics. In reality, it contains the only mistery. (R. Feynman).

Feynman has imagined to fire electrons one by one through a double slit and then reveal the position where each electron strikes a screen behind the slits. Each electron behave like particle because they arrive  in “lumps” to the detection screen.  After many electrons have passed through the slits, one can observe the interesting diffraction pattern showing the wave behaviour of each electron. If one slit is closed and electron can passes only through the other slit the diffraction pattern disappears. What is crucial in Feynman’s thought experiment is that each electron behaves like a wave and also it is not possible to say through which slit the electron is passed.

We should say right away that you should not try to setup this experiment. This experiment has never been done in just this way. The trouble is that the apparatus would have to be made on an impossibly small scale to show the effects we are interested in (R. Feynman)

Are you joking Mr. Feynman ? Herman Batelaan of the University of Nebraska-Lincoln and colleagues have created a double slit experiment that realize the procedure of Feynman’s thought experiment. Scientists created a double slit in a gold-coated silicon membrane, in which each slit is 62 nm wide and 4 μm long with a slit separation of 272 nm. To block one slit at a time, a tiny mask controlled by a piezoelectric actuator was used.
The electrons were created at a tungsten filament and accelerated across 600 V and then collimated into a beam. After passing through the double slit, they were  imaged on a two-dimensional microchannel plate and phosphorus screen.
Scientist were able to slow electrons emission rate in order to observe individual electrons  passing through the slits

Simplified experimental setup. Credit Roger Bach et al 2013 New J. Phys. 15 033018

Simplified experimental setup. (Credit Roger Bach et al 2013 New J. Phys. 15 033018)

The diffraction pattern was seen when the electrons had access to both slits, but not seen when one slit was blocked. You can see the formation of the diffraction in this spectacular video

Buildup of electron diffraction (Credit Roger Bach et al 2013 New J. Phys. 15 033018)

You can read for free the original paper: Bach R., Pope D., Liou S.H. and Batelaan H. “Controlled double-slit electron diffraction”, New Journal of Physics, 15, (2013), at this link

Further reading
Feynman R.P., “The Feynman Lectures on Physics” , vol. III, cap. I Quantum Behavior.


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