New technique revolutionizes materials research in quantum computing

Quantum computing continues to develop, but the discipline still suffers from an overall stability problem.

If the notion of quantum computing is still relatively abstract for part of the public, it would be easy to forget that the underlying theory, as abstract as it is for the general public, is also full of very concrete implications. But it is still necessary to be able to apply this theory in practice, and overall, it is at this level that the shoe pinches. But the deal could change thanks to researchers at the University of Pennsylvania.

As things stand, one of the main obstacles to the development of quantum computing is on the materials side. Because to produce the logical units of a quantum processor, researchers absolutely need a compound that brings together two rare features: quantum entanglement and coherence.

Entanglement, a “frightening” but also fascinating phenomenon

The first designates very summarily a quantum state where two particles are linked by an inextricable link independent of their distance; technically, if one of the two particles undergoes the slightest modification, the other member of the tandem will undergo precisely the same effects, even if it is located at the other end of the universe. This notion gave rise to a famous phrase by Albert Einstein, who designated quantum entanglement as a “remote spooky action”.

Today, the concept is much better understood than in the days of the brilliant theorist. It is a concept that is the basis of the operation of quantum computers today, or more precisely of the logical units on which they are based, the quantum bits – or qbits. Unlike the standard bits you handle every day on your computers, smartphones and other computing devices, qbits can co-exist in multiple states simultaneously – much like Schroedinger’s famous cat which is often used to illustrate this concept. It is this feature that allows a quantum computer to process phenomenal amounts of data in a relatively short time on the scale of a standard computer.

Maintaining entanglement, the quantum computing challenge

The concept itself may seem extremely abstract, but it is an aspect on which researchers are beginning to have real expertise; there are many experimental quantum computers in operation today. On the other hand, the situation is different when the second parameter mentioned above, namely consistency, is taken into account.

Because producing many quantum entanglements is not enough; they also have to be maintained over time, and that’s much more complicated. So complicated, in fact, that this parameter alone is enough to explain the relatively slow development of this technology, at least as far as consumer applications are concerned.

Specialists therefore seek again and again to develop a revolutionary material, capable both of enabling entanglement, but also of maintaining it. And this is precisely what researchers at the University of Pennsylvania are claiming with a very particular material: a semi-metal with the formula Ta2NiSe5.

A new study technique for quantum candidates

The latter was subjected to a new technique called the circular photogalvanic effect, which is based on the transfer of an electric field by a light wave. This review has explored its relevant properties in the context of a quantum computer; he revealed a strange peculiarity of this material IN effect, it has a form of symmetry which, when present in a crystal, prevents it from reacting to the circular photogalvanic effect; yet Ta2NiSe5 responds well to this effect as it exhibits this symmetry.

The researchers deduced that Ta2NiSe5 tended to lose its symmetry at very low temperatures. Under these conditions, we pass from a so-called orthorhombic structure (where each mesh of the crystal lattice is a cube) to a so-called monoclinic structure.

This is a discovery that might seem perfectly anecdotal, but it is more substantial than it seems at first glance. Indeed, this work defines a new tool that researchers will now be able to use to study other very complex crystalline matrices; with a little luck, some of them will express a phenomenon of quantum entanglement with great coherence – two elements which, as mentioned above, are essential for the proper functioning of quantum computers.

According to one of the study authors quoted by Slashgear, “these entangled states of matter“could well become”natural platforms on which we could perform large-scale quantum simulations”. If this work will not make it possible to produce a quantum computer for the general public in the near future, it is undoubtedly a question a significant step in this direction.

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