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Over 240 years ago, famous mathematician Leonhard Euler came up with a question: if six army regiments each have six officers of six different ranks, can they be arranged in a square formation such that no row or column repeats either a rank or regiment?

After searching in vain for a solution, Euler declared the problem impossible – and over a century later, the French mathematician Gaston Tarry proved him right. Then, 60 years after that, when the advent of computers removed the need for laboriously testing every possible combination by hand, the mathematicians Parker, Bose, and Shrikhande proved an even stronger result: not only is the six-by-six square impossible, but it’s the only size of square other than two-by-two that doesn’t have a solution at all.

Most quantum computers are based on superconductors or trapped ions, but an alternative approach using ordinary atoms may have advantages.


Back in 2016, we told you about the iBubble, an underwater drone that autonomously follows and films scuba divers. Well, it now has a more capable industrial-use big brother, known as the Seasam.

‘Geometric frustration’ can cause the electrons in materials with atoms arranged in a triangular pattern to organize in three competing ways simultaneously, reveals a new computational study led by researchers at the Flatiron Institute.

Materials that look like mosaics of triangular tiles at the atomic level sometimes have paradoxical properties, and quantum physicists have finally found out why.

Using a combination of cutting-edge computational techniques, the scientists found that under special conditions, these triangular-patterned materials can end up in a mashup of three different phases at the same time. The competing phases overlap, with each wrestling for dominance. As a result, the material counterintuitively becomes more ordered when heated up, the scientists reported in Physical Review X.

An experiment, performed by Istituto Nazionale di Ricerca Metrologica (INRIM) on 200 km of the Italian Quantum Backbone, in collaboration with Toshiba Europe, shows that coherent laser interferometry considerably improves the performances of quantum key distribution protocols in long-distance, real-world networks. The study has been published in Nature Communications.

Quantum Key Distribution (QKD) protocols enable cryptographic keys to be shared between distant parties with an intrinsic security guaranteed by the laws of quantum mechanics. This is made possible by the transmission of single photons, the elementary particles of which light is made of.

The interest for this subject extends well beyond the scientific community, and has now a strong strategic and commercial relevance. The European Commission, within the “European Quantum Communication Infrastructure” intitative, aims at integrating quantum key distribution technologies into specific services throughout the European Union within the next 10 years, and INRIM will take part in the design of this infrastructure with the OQTAVO project.

A surprising property of how resonant photons interact with an absorbing medium has been uncovered by physicists in Canada. They say they have found that even photons passing straight through the medium energize atoms within it, causing atoms to spend nearly as much time in their excited states as those that have absorbed photons. They see their result as a challenge to theorists trying to describe how light interacts with matter quantum mechanically.

Aephraim Steinberg and colleagues at the University of Toronto made the discovery while investigating what happens to a beam of photons passing through a cloud of atoms when the photons’ frequency is equal to that of one of the atomic transitions. Intuitively, they say, it would be expected that those photons exciting atoms within the cloud would be absorbed and then at best re-emitted in a random direction. As such, the flux of photons coming from excited atoms that are detected in the forward direction would be miniscule.

Indeed, they point out, this idea that only absorbed, or “lost”, photons contribute to the excitation springs naturally from theory that tells us the total time atoms spend in the excited state is directly proportional to the number of photons that are lost.

Computers play an important role in many aspects of life today. Digital computers are the most widely used, while quantum computers are well known. However, the least known computers are the so-called Stochastic Pulse Computers. Their work is based on highly parallel logical operations between trains of electrical pulses, where the pulses occur at random times, as in neurons, the nerve cells in the brains of humans and mammals.

Researchers from the Institute of Photonics and Nanotechnologies of the Cnr and the Politecnico di Milano have built a battery which, following the laws of quantum physics, has a recharge time that is inversely related to the amount of stored energy.

Quantum batteries are a new class of energy storage devices that operate according to the principles of quantum physics, the science that studies the infinitely small where the laws of classical physics do not always apply. Tersilla Virgili of the Institute of Photonics and Nanotechnologies of the National Research Council (Cnr-Ifn) and Giulio Cerullo of the Physics Department of the Politecnico di Milano have shown that it is possible to manufacture a type of quantum battery where the charging power increases faster by increasing the battery capacity. The work, carried out together with other international research groups, was published in Science Advances.

“Quantum batteries have a counter-intuitive property in which the recharge time is inversely related to the battery capacity, that is the amount of stored electrical charge,” explains Virgili. “This leads to the intriguing idea that the charging power of quantum batteries is super-extensive, meaning that it increases faster with battery size.”

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