A classic quantum experiment that shows how particles can behave like waves has been demonstrated with atoms for the first time, something that was thought to be impossible. The finding could be used to design atomic detectors that can measure gravitational waves that can鈥檛 be detected with current technology.
In 1927, physicist George Paget Thomson showed that electrons passing through a crystal would diffract, producing a distinctive pattern that occurs when a wave squeezes through a small opening and then bends its path, spreading outwards. In this case, the pattern was caused by the electrons passing through gaps in the crystal鈥檚 structure, called a grating.
This experiment, , was a key piece of evidence showing that subatomic particles are partly wave-like, and also helped enable the development of the electron microscope.
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A diffraction pattern for atoms was demonstrated a few years afterwards, but this instead involved reflecting atoms off a surface. 快猫短视频s later worked out how to diffract atoms through gratings, but these had to be specially designed using a similar process to making computer chips. The gaps in these gratings were much larger than crystal gratings, which fundamentally limited the sensitivity of the diffraction patterns.
Diffracting atoms through a crystal grating, as in the case of the electron, would allow for much larger, and so more sensitive, patterns, but it was thought to be impossible because the high-energy atoms required would damage the crystal grating and diffraction couldn鈥檛 take place.
Now, at the German Aerospace Center and his colleagues have diffracted helium and hydrogen atoms through a crystal grating in the form of a graphene sheet, a one-atom-thin layer of carbon atoms.
Brand and his team first accelerated hydrogen or helium atoms in a narrow beam to high speeds, and energies, because it had previously been shown that room-temperature hydrogen and helium couldn鈥檛 pass through graphene. Then they fired the high-energy atoms at the graphene sheet, which they thought should have been damaged.
However, after 100 hours of irradiation from the atom beam, Brand and his colleagues recorded no damage to the sheet. Instead, they observed the distinctive circular ring patterns produced from diffraction when they placed a camera on the other side.
Giving the atoms higher energies is what allows them to squeeze through the graphene gaps, says at the University of Cambridge, because they can exchange energy with the graphene鈥檚 atoms in an undetectable way. If the energy exchange were detectable, then the wave nature of the atoms would be disturbed, by the laws of quantum mechanics, and the diffraction pattern would no longer occur.
This can be thought of as a room with many doorways that are typically closed, but that at higher energies become open. 鈥淚 can only get through if I open a door, and that takes energy. If I am clumsy, like a drunk teenager, then everyone will know which door I used and there will then be no diffraction. If I open the door and then close it deftly without losing or gaining energy, then no one, including me, knows which door I used and therefore there will be diffraction,鈥� says Allison.
This effect could be used to build an atomic interferometer, like the one used in the Laser Interferometer Gravitational-Wave Observatory, but with far higher precision and sensitivity than current techniques allow, says Allison. 鈥淚t鈥檚 brilliant work and I鈥檓 impressed the authors tried such an audacious experiment.鈥�
arXiv
