Massive particles test standard quantum theory

August 11, 2017
Comparing the diffraction patterns behind a combination of precisely written slits allows testing quantum mechanics with complex molecules. Credit: Group for Quantum Nanophysics, Faculty of Physics, University of Vienna; Image-Design: Christian Knobloch

In quantum mechanics particles can behave as waves and take many paths through an experiment. It requires only combinations of pairs of paths, rather than three or more, to determine the probability for a particle to arrive somewhere. Researchers at the universities of Vienna and Tel Aviv have addressed this question for the first time explicitly using the wave interference of large molecules behind various combinations of single, double, and triple slits.

Quantum mechanics describes how matter behaves on the smallest mass and length scales. However, the absence of quantum phenomena in our daily lives has triggered a search for minimal modifications of , which might only be noticeable for . One candidate is to search for so-called higher-order . In , the resulting from an arbitrary number of non-interacting open paths can always be described by all combinations of pairs of paths. Any remaining pattern would be due to higher-order interference and be a possible indicator for new physics.

While this rule has been tested before with light and microwave radiation, researchers at the Universities of Vienna and Tel Aviv have now run for the first time a dedicated experiment with massive . "The idea has been known for more than twenty years. But only now do we have the technological means to bring all the components together and build an experiment capable of testing it with massive molecules," says Christian Brand, one of the authors of the study.

Multi-slit matter wave diffraction

In their experiments at the University of Vienna, researchers of the Quantum Nanophysics Group headed by Markus Arndt prepared as matter waves. This was achieved by evaporating them from a micron-sized spot in high vacuum and letting them evolve freely for some time. After a while, each molecule delocalized, spreading across many places at once. This means that when each molecule encounters a mask containing multiple slits, it can traverse many of the slits in parallel. By carefully comparing the position of molecules arriving at the detector behind a combination of single-, double- and triple slits they were able to place bounds on any multipath contribution.

Nanofabrication enabling technology

A crucial component of the experiment is the mask - an ultra-thin membrane into which arrays of single-, double- and triple-slits were fabricated. It was designed and fabricated by Yigal Lilach and Ori Cheshnovsky at Tel Aviv University. They had to engineer a diffraction mask, where the maximum deviation in the slit dimensions was not much larger than the size of the molecules it was diffracting. The mask was integrated in the Vienna laboratory and the researchers studied a broad range of molecular velocities in the same experimental run. For all of them, the scientists found the interference pattern to follow the expectations of standard mechanics with an upper bound in the deviation of less than one particle in a hundred. "This is the first time an explicit test of this kind has been conducted with massive particles", says Joseph Cotter, the first author of this publication. "Previous tests have pushed the frontiers with single photons and microwaves. In our experiment, we put bounds on higher-order interference of massive objects."

The study is published in Science Advances.

Explore further: Physicists build stable diffraction structure in atomically thin graphene

More information: "In search of multipath interference using large molecules" Science Advances

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1 / 5 (2) Aug 14, 2017
QM is not a theory.
not rated yet Aug 14, 2017
This means that when each molecule encounters a mask containing multiple slits, it can traverse many of the slits in parallel
Such an interpretation could work for some volatile shapeless photons but at the case of dye molecules such a model looks like particular nonsense: the complex system like the dye molecule cannot disassemble itself during traveling through both slits and to restore again into original shape just after it. The probability of such process would be very low, not to say, the decomposing of such a molecule would require much higher energies. According to pilot wave interpretation of QM of Louis deBroglie it's only the wake wave of vacuum formed around particle during its motion, what passes both slits at the same moment - and just the experiments like this one above illustrate it clearly.
not rated yet Aug 14, 2017
Another clue for deBroglie model bring the results of experiment itself - under magnification of the above picture we can see, how the red diffraction pattern on the right is actually composed of myriads of tiny spots formed with individual dye molecules after their impact at the target. This is not what the above interpretation predicts. Standard QM doesn't predict formation of any spots at the target - only intensity of smooth diffuse interference patterns. The same result follows from water surface analogy of double slit experiment - yet the wrong interpretation presented above remains perpetuated even after ten years after its publishing, because it brings the tabooed notion of vacuum like the massive elastic environment for particle spreading.
not rated yet Aug 14, 2017
Didn't you get the memo? There are ONLY waves and the center of waves.
not rated yet Aug 20, 2017
Sad to see that the author sells the awkward many worlds picture in even cases where its absurdity is obvious. There are new insights on quantum measurement and interpretation, studying them helps to stop overinterpreting the formalism.

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