This week in science: 16 million entangled atoms, and baryonic matter

This week in science is a review of the most interesting scientific news of the past week.

Partial view of the source producing the single photon. Credit: UNIGE.

Entanglement of 16 million atoms demonstrated

Quantum entanglement, a physical phenomenon predicted by the quantum mechanics theory, occurs when a pair or a group of particles interact in a way that the quantum state of each particle cannot be described independently of the others. Interestingly, this dependence occurs even when the particles are separated by large distances, what could be used in the future for the development of new communication and computing techniques.

However, not much experimental evidence of the existence of quantum entanglement was available until recently, despite some advances that showed the entanglement of 2,900 atoms. But last week, scientists at the University of Geneva (UNIGE), Switzerland, have announced their findings demonstrating that 16 million atoms were entangled in a one-centimeter crystal. The scientists have managed to obtain this result in an indirect way, because, as stated by Florian Fröwis, a researcher at UNIGE:

It's impossible to directly observe the process of entanglement between several million atoms since the mass of data you need to collect and analyze is so huge.

It is known from the theory that when a photon penetrates a crystal, it causes the atoms it traverses to entangle before being re-emitted. By analyzing the characteristics, statistical properties and the probabilities of the re-emitted photon, they were then able to determine the amount of 16 million entangled atoms.

The upcoming quantum revolution, which is being led by teams of scientists in research institutions and companies around the world, benefits directly by the properties of quantum entanglement. Therefore, this achievement marks a milestone in the area.


Cosmic microwave background. Credit: NASA / WMAP Science Team [Public domain], via Wikimedia Commons

Evidence of missing baryonic matter

Baryonic matter includes nearly all matter we experience in our daily lives and encompasses atoms of any sort, providing them with the property of mass. Non-baryonic matter includes neutrinos, free electrons, and dark matter.

This kind of matter plays a huge role in theories such as that of the Big Bang, in which it is assumed that the initial explosion produced a state with equal amounts of baryons and antibaryons. Unfortunately, according to calculations made by scientists of how much baryonic matter should exist in the universe right now, approximately 50 percent of it is missing.

One of many theories that try to explain where all that matter is hiding proposes that it exists as strands of baryonic matter floating in the space between galaxies. Also, because of this particular arrangement, it cannot be seen with conventional instruments, a major issue for its detection.

But scientists from two independent teams, one from the Institute of Space Astrophysics and another from the University of Edinburgh have managed to detect the baryonic matter by taking advantage of a phenomenon called the Sunyaev-Zel'dovich effect. This effect occurs when light left over from the Big Bang scatters as it passes through hot gas and therefore would make it possible to indirectly detect the baryonic matter in the cosmic microwave background.

Each team was able to create maps of where baryonic matter strands might exist between two galaxies by picking pairs of galaxies to study. The process was repeated a million times by one team and 260,000 times by the other, and both of them used data from the Planck Collaboration.

Results from both groups were positive and they claim to have found evidence of the theorized filaments of baryonic matter between galaxies. One difference in their findings was the density of those filaments - one team has found it to be three times as dense as the mean of observable matter while the other team has found it to be six times as dense. However, they explained this result was expected and due to differences in the distances from the chosen galaxies.


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