The ‘cúdits’: the promising and alternative ‘language’ of quantum computers

Computers speak in ones and zeros. They are called bits. It is the basis of computational communication, in which they operate from mobile phones and computers at home to the chocolate machine at work. It is not the most effective system, but it is the simplest, hence its enormous success. That is why quantum computing, despite following a totally different system, has ‘adopted’ this binary system: quantum bits (also called qubits), can be ones and zeros at the same time. That is why its processing capacity is exponentially larger. “However, the building blocks of quantum computers are more than just zeros and ones,” explains Martin Ringbauer, an experimental physicist from Innsbruck, Austria. “Restricting them to binary systems prevents these devices from reaching their true potential.” Ringbauer knows what he is talking about, since he is one of the members of the team led by Thomas Monz , at the Department of Experimental Physics at the University of Innsbruck, and who has managed to develop a quantum computer that can perform arbitrary calculations with another ‘language. ‘ different and more effective: the cúdits . Physics makes a difference We normally use decimal numeration (in base ten, like the number of fingers on our hands) in our daily lives. However, there are other types, from sexagesimal (based on 60, in which time is measured) to the aforementioned binary numbering (ones and zeros). The simplicity of the latter makes it a reliable and error-resistant system, the biggest problem with classic computers. However, nature goes beyond ones and zeros. Especially in the curious quantum world, where things are and are not at the same time, like the famous Schrödinger’s cat (alive and dead at the same time). For example, the Innsbruck system, just explained in a paper published in ‘Nature Physics’, is based on individual calcium atoms where information is trapped. But each of these atoms naturally has eight different states, only two of which are used to store information and produce qubits. The rest is ‘ignored’. Since the 1990s, there has been a whole theoretical base that states that all these ‘compartments’ or states can be used to store more information and, therefore, carry out tasks with fewer operations than with the binary system. They are called cúdits. The team’s achievement has been to use up to seven of those states for a single quantum operation and, according to the study, maintain. “Qubits (two states) and qudits (more than two states) aren’t really that different,” says Ringbauer. “The properties that we know of quantum systems, such as sensitivity to external influences, largely remain the same, whether you use those quantum systems as qubits or qudits.” A ‘language’ for (almost) all systems However, contrary to the classical case, using more states does not make the computer less reliable. “Quantum systems naturally have more than two states and we show that we can control all of them equally well,” says Thomas Monz. “It’s important to note that cudit levels are there anyway, whether they’re used or not,” says Ringbauer. This is different from classical systems, which we tend to build with as many states as we need. Of course, using all of these states for computation presents many additional hurdles, because each level responds differently to external influences, and because we need to find new ways to interact with them. All of this was a challenge in creating the quantum computer, but once solved, there is no reason why a qudit would perform worse than a qubit.” On the other hand, many of the tasks that require quantum computers, such as problems in physics, chemistry, or materials science, are also naturally expressed in the cudit language. Rewriting them for qubits can often make them too complicated for current quantum computers. “Working with more than zeros and ones is very natural, not only for the quantum computer but also for its applications, allowing us to unlock the true potential of quantum systems,” explains Ringbauer. MORE INFORMATION This red dot is 13.5 billion years old and is the oldest galaxy ever observed Webb’s new surprise: the telescope reveals the mysterious and dusty center of the ‘perfect galaxy’ NGC 628 And not only the system of trapped atoms operates in more of two states. It’s the same with most systems: from superconducting to photonic systems, so it would be a suitable ‘language’ for almost all equipment. “There is still a lot of unused potential in current quantum hardware, and using cúdits is a way to unlock some of this potential to build more efficient and powerful quantum computers,” concludes the researcher.