Decoherence is the biggest problem for quantum computers. This superconductor wants to put an end to it

Decoherence is the weakest point of current quantum computer prototypes. However, before delving into it, we would like to briefly review What is quantum entanglement?This phenomenon has no equivalent in classical physics, and consists in the fact that the state of the quantum systems involved, which can be two or more, is the same. This means that these objects are actually part of the same system, even if they are physically separated. In fact, the distance does not matter.

If two particles, objects or systems are entangled by this quantum phenomenon, when we measure the physical properties of one of them we will be instantly influencing the physical properties of the other system with which it is entangled. Even if it is at the other end of the universe. As strange and surprising as this phenomenon may seem to us, it has been empirically proven. In fact, it is, along with the superposition of states, one of the fundamental principles of quantum computing.

The Achilles heel of quantum computers

A promise is a promise, so we are now ready to delve into the concept of quantum decoherence. This phenomenon occurs when the conditions necessary for a system in an entangled quantum state to remain in place disappear. A perhaps slightly simpler way of describing it is to see it as a system that stops behaving as dictated by the rules of quantum mechanics when certain conditions are met, and from that moment on begins to behave as dictated by the rules of classical physics.

When quantum decoherence appears, quantum effects disappear. And, therefore, so do the advantages they bring in the context of quantum computing. This phenomenon is very important because it helps us understand why many macroscopic physical systems do not exhibit quantum effects. Or, what is the same, why in our everyday environment We cannot observe the counterintuitive effects of quantum mechanics. However, many scientists researching quantum computers are trying to find an effective way to deal with decoherence.

The approach taken by Professor Peng Wei and his team at the University of California in Riverside (USA) is very original. These scientists have come up with the idea of ​​developing a topological superconductor with the aim of providing quantum computers with the robustness they need to process information correctly. It is not easy to explain in a simple way what a topological superconductor is, but in this article we need to be at least minimally familiar with them. As we can guess, one of their fundamental properties is superconductivity, so that in certain circumstances the electric current can flow through them without any resistance, and therefore without any of the energy being transformed into heat.

On the other hand, topology is a branch of mathematics that studies the characteristics of objects whose properties are not altered when they undergo a certain deformation. Topological superconductors, therefore, are capable of conducting electric current without resistance, and, at the same time, have unusual properties derived from their topology. The most important is that they can host Majorana fermions both on their surface and on their edges. These fermions have an astonishing property: they are both a particle and their own antiparticle.

What makes them very attractive for quantum computing is that, when they do occur, they theoretically occur in pairs and have reasonably high stability, something that is not common in the world of particles subject to the laws of quantum mechanics. This property can theoretically be used to store quantum information in two different places. The coincidence of this duplicity and their stability suggests that these particles could be used to make qubits that are more stable and less prone to external perturbations than the qubits used in current quantum computers.

“A topological superconductor uses a delocalized state of an electron or hole to carry quantum information and process data robustly (…) Our material could be a promising candidate for developing more scalable and reliable quantum computing components,” explains Professor Peng Wei. It sounds great, but that’s not all. His superconductor has been shown to have great stability in the presence of magnetic fields, and, in addition, removes sources of decoherence caused by material defects, something that until now represented an enormous challenge. It is reasonable to expect that we may be witnessing one of the great advances in quantum computers in recent years.

Imagen | IBM

More information | Interesting Engineering

At WorldOfSoftware | The arrival of error correction to quantum computers is complicated. Although not all is lost