Three 'twisted' photons in three dimensions
Researchers at the Institute of Quantum Optics and Quantum Information, the University of Vienna, and the Universitat Autonoma de Barcelona have achieved a new milestone in quantum physics: they were able to entangle three particles of light in a high-dimensional quantum property related to the 'twist' of their wave front structure. The results from their experiment appear in the journal Nature Photonics.
Entanglement is a counterintuitive property of quantum physics that has long puzzled scientists and philosophers alike. Entangled quanta of light seem to exert an influence on each other, irrespective of how much distance is between them. Consider for example a metaphorical quantum ice dancer, who has the uncanny ability to pirouette both clockwise and counter-clockwise simultaneously. A pair of entangled ice-dancers whirling away from each other would then have perfectly correlated directions of rotation: If the first dancer twirls clockwise then so does her partner, even if skating in ice rinks on two different continents.
"The entangled photons in our experiment can be illustrated by not two, but three such ice dancers, dancing a perfectly synchronized quantum mechanical ballet," explains Mehul Malik, the first author of the paper. "Their dance is also a bit more complex, with two of the dancers performing yet another correlated movement in addition to pirouetting. This type of asymmetric quantum entanglement has been predicted before on paper, but we are the first to actually create it in the lab."
Tetra quarks: New four-flavour particle discovered
Scientists on the DZero collaboration at the US Department of Energy's Fermi lab have discovered a new particle – the latest member to be added to the exotic species of particle known as tetra quarks.
Quarks are point-like particles that typically come in packages of two or three, the most familiar of which are the proton and neutron (each is made of three quarks). There are six types, or "flavours," of quark to choose from: up, down, strange, charm, bottom and top. Each of these also has an antimatter counterpart.
Over the last 60 years, scientists have observed hundreds of combinations of quark duos and trios.
In 2008 scientists on the Belle experiment in Japan reported the first evidence of quarks hanging out as a foursome, forming a tetra quark. Since then physicists have glimpsed a handful of different tetraquark candidates, including now the recent discovery by DZero – the first observed to contain four different quark flavours.
DZero is one of two experiments at Fermi lab's Tevatron collider. Although the Tevatron was retired in 2011, the experiments continue to analyze billions of previously recorded events from its collisions.
As is the case with many discoveries, the tetra quark observation came as a surprise when DZero scientists first saw hints in July 2015 of the new particle, called X(5568), named for its mass – 5568 megaelectronvolts.