Fermions do not travel together, theory proved

March 10, 2007

Fermions tend to avoid each other and cannot "travel" in close proximity. Demonstrated by a French team at the Institut d'optique (CNRS), this result is described in detail in the January 25, 2007 issue of Nature. It marks a major advance in our understanding of phenomena at a quantum scale.

For many years, the theory of quantum mechanics stipulated that certain particles, the fermions , were incapable of "travelling" in close proximity. For example, in a jet of identical particles, the theory supposed that the distance between them was always greater than a given value, called the "correlation length".

Scientists in the Charles Fabry Laboratory at the Institut d'optique, working with a team from the Free University in Amsterdam, have recently shown that this "anti-bunching" property, which it had never been possible to demonstrate hitherto, does indeed exist. It is as if the particles repel each other, even though interactions between them are negligible. In fact, this "anti-bunching" is due to quantum interferences which forbid the probability of finding two very close particles.

To arrive at this conclusion, the scientists compared the behaviour of fermions with that of bosons , under identical conditions. Amongst the latter, the same interferences led on the contrary to a "bunching" effect, and thus an increased probability of finding two particles together.
The experiments at the Institut d'optique were performed using the same system (which ensured identical conditions) on two helium isotopes.

In this situation, the scientists demonstrated the correlation length of fermions, which was close to a millimetre. This effect was anticipated, but its demonstration constitutes an advance in our ability to detect correlations between atoms, and thus a further step towards understanding the behaviour of matter at the quantum scale.

Citation: Comparison of the Hanbury Brown–Twiss effect for bosons and fermions, T. Jeltes, J. M. McNamara, W. Hogervorst, W. Vassen, V. Krachmalnicoff, M. Schellekens, A. Perrin, H. Chang, D. Boiron, A. Aspect & C. I. Westbrook. Nature, 2007, Vol. 445, No. 7126

Source: CNRS

Explore further: Physicists collide ultracold atoms to observe key quantum principle

Related Stories

Cold fermions keep distance from each other

January 4, 2016

Today, quantum optical experiments provide methods to prove the rules that have been thought of and pressed into elegant mathematical equations in those days. In this regard, scientists in the Quantum Many-Body Division of ...

Third research team close to creating Majorana fermion

March 16, 2012

(PhysOrg.com) -- Recently there has been a virtual explosion of research efforts aimed at creating the elusive Majorana fermion with different groups claiming to be near to creating them. First there was news that a team ...

Neutrons uncover new density waves in fermion liquids

March 28, 2012

Scientists working at the Institut Laue-Langevin, one of the world's leading centres for neutron science, have carried out the first investigation of two-dimensional fermion liquids using neutron scattering, and discovered ...

Recommended for you

Counting down to the new ampere

August 29, 2016

After it's all over, your lights will be just as bright, and your refrigerator just as cold. But very soon the ampere—the SI base unit of electrical current—will take on an entirely new identity, and NIST scientists are ...

Measuring tiny forces with light

August 25, 2016

Photons are bizarre: They have no mass, but they do have momentum. And that allows researchers to do counterintuitive things with photons, such as using light to push matter around.

0 comments

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

Click here to reset your password.
Sign in to get notified via email when new comments are made.