The atom without properties

The atom without properties
A microchip is used to trap a cloud of ultracold atoms and to entangle the atoms' magnetic moments. Credit: University of Basel, Department of Physics

The microscopic world is governed by the rules of quantum mechanics, where the properties of a particle can be completely undetermined and yet strongly correlated with those of other particles. Physicists from the University of Basel have observed these so-called Bell correlations for the first time between hundreds of atoms. Their findings are published in the scientific journal Science.

Everyday objects possess properties independently of each other and regardless of whether we observe them or not. Einstein famously asked whether the moon still exists if no one is there to look at it; we answer with a resounding yes. This apparent certainty does not exist in the realm of small particles. The location, speed or magnetic moment of an atom can be entirely indeterminate and yet still depend greatly on the measurements of other distant atoms.

Experimental test of Bell correlations

With the (false) assumption that atoms possess their properties independently of measurements and independently of each other, a so-called Bell inequality can be derived. If it is violated by the results of an experiment, it follows that the properties of the atoms must be interdependent. This is described as Bell correlations between atoms, which also imply that each atom takes on its properties only at the moment of the measurement. Before the measurement, these properties are not only unknown - they do not even exist.

A team of researchers led by professors Nicolas Sangouard and Philipp Treutlein from the University of Basel, along with colleagues from Singapore, have now observed these Bell correlations for the first time in a relatively large system, specifically among 480 atoms in a Bose-Einstein condensate. Earlier experiments showed Bell correlations with a maximum of four light particles or 14 atoms. The results mean that these peculiar quantum effects may also play a role in larger systems.

Large number of interacting particles

In order to observe Bell correlations in systems consisting of many particles, the researchers first had to develop a new method that does not require measuring each particle individually - which would require a level of control beyond what is currently possible. The team succeeded in this task with the help of a Bell inequality that was only recently discovered. The Basel researchers tested their method in the lab with small clouds of cooled with laser light down to a few billionths of a degree above absolute zero. The atoms in the cloud constantly collide, causing their magnetic moments to become slowly entangled. When this entanglement reaches a certain magnitude, Bell correlations can be detected. Author Roman Schmied explains: "One would expect that random collisions simply cause disorder. Instead, the quantum-mechanical properties become entangled so strongly that they violate classical statistics."

More specifically, each atom is first brought into a quantum superposition of two states. After the atoms have become entangled through collisions, researchers count how many of the atoms are actually in each of the two states. This division varies randomly between trials. If these variations fall below a certain threshold, it appears as if the have 'agreed' on their measurement results; this agreement describes precisely the Bell correlations.

New scientific territory

The work presented, which was funded by the National Centre of Competence in Research Quantum Science and Technology (NCCR QSIT), may open up new possibilities in quantum technology; for example, for generating random numbers or for quantum-secure data transmission. New prospects in basic research open up as well: "Bell correlations in many-particle systems are a largely unexplored field with many open questions - we are entering uncharted territory with our experiments," says Philipp Treutlein.


Explore further

All quantum communication involves nonlocality

More information: Bell correlations in a Bose-Einstein condensate, Science, DOI: 10.1126/science.aad8665
Journal information: Science

Citation: The atom without properties (2016, April 21) retrieved 19 July 2019 from https://phys.org/news/2016-04-atom-properties.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
190 shares

Feedback to editors

User comments

Apr 22, 2016
JUST Pull near near to earth. Let it still orbit around. 150 miles distance should be O.K

Apr 22, 2016
JUST Pull near near to earth. Let it still orbit around. 150 miles distance should be O.K

W.T.F.?

The holy triffecta:
Incoherent, incomprehensible and not related to the article at all. Well done!

Apr 22, 2016
An article that actually gets the Bell inequality and its implications closer to right than wrong? I'm shocked. Shocked!

Apr 22, 2016
JUST Pull near near to earth. Let it still orbit around. 150 miles distance should be O.K

THE MOON, I Wrote.

Apr 22, 2016
This comment has been removed by a moderator.

Apr 23, 2016
Einstein famously asked whether the moon still exists if no one is there to look at it; we answer with a resounding yes.


Only because of confusion in the language. The answer turns to be slightly more complicated, because the fundamental idea breaks down to: "If there is nothing observing the photons reflected off of the moon, does the moon exist?".

The same Einstein's relativity that says there's no fixed universal location or time that would be independent of observer, also says you can't meaningfully say that something exists until you interact with it and recieve information of it, and so if nobody and nothing sees the moon, the moon doesn't exist - or from an alternate point of view - nothing but the moon exists. The question cannot be answered with a yes or no.

So the building blocks of all matter have no properties which dictate the structure of said matter


The properties arise out of interaction, not inherently. A molecule of water is not wet.

Apr 23, 2016
Believe it or not, matter actually does exist whether other matter interacts with it or not, matter with finite physical properties...Jesus.


The fundamental point is like 1 + 2 makes 3 even if there is no 3 lurking in either 2 or 1. The property of being the number three is not inherent to anything in the system, yet it becomes so when put together. Or, take two straight sticks and cross them - that's a new property. There's no "crossness" in the sticks themselves, yet it arises out of the interaction.

The question is simpy figuring out what is really there - what's the real fundamental thing that actually exists at the base of everything - the one thing that gives rise to all the different combinations.

Apr 25, 2016
Hmmm...ok, assuming I'm getting what I'm meant to from this article, I can't help but wonder what would happen to a single atom corraled in a gigantic, super-cooled vacuum chamber. Would it evaporate into nothing? Would the interactive "measurement" of its constituent particles be sufficient to maintain it in its material form? Would the laser grid necessary to confine the atom negate any possibility of retrieving useful data about its apparently conditional state of reality?

Apr 25, 2016
Hmmm...ok, assuming I'm getting what I'm meant to from this article, I can't help but wonder what would happen to a single atom corraled in a gigantic, super-cooled vacuum chamber.

Think hydrogen (in space)
Would it evaporate into nothing?

Do hydrogen atoms?
or any other atom sized particles, for that matter...)

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more