Any leap forward in quantum computing multiplies the potential of a technology capable of performing calculations and simulations that go beyond the scope of current computers while facilitating the study of phenomena that until now have only been theoretical. .
Last year, a group of researchers put forward the idea in the newspaper Nature that an alternative to quantum theory based on real numbers can be experimentally falsified. The original proposal was a challenge that was taken up by the leading scientist in the field, Jian-Wei Pan, with input from physicist Adán Cabello, of the University of Seville. Their combined research demonstrated “the indispensable role of complex numbers [square root of minus one, for example] in standard quantum mechanics. The results make it possible to progress in the development of computers using this technology and, according to Cabello, “to test quantum physics in hitherto inaccessible regions”.
Jian-Wei Pan, 51, graduated in 1987 from the University of Science and Technology of China (USTC) and holds a doctorate from the University of Vienna, leads one of the largest quantum research teams and most powerful in the world, and has been described by physics Nobel laureate Frank Wilczek as “a force of nature”. Thesis supervisor of Jian-Wei Pan at the University of Vienna, physicist Anton Zeilingeradded: “I can’t imagine the emergence of quantum technology without Jian-Wei Pan.”
Pan’s leadership in research was fundamental. “The experiment can be seen as a game between two players: real-valued quantum mechanics versus complex-valued quantum mechanics,” he explains. “The game is played on a quantum computing platform with four superconducting circuits. By sending random measurement bases and measuring the result, the game score is obtained, which is a mathematical combination of the measurement bases and the result. The rule of the game is that real-valued quantum mechanics is excluded if the game score exceeds 7.66, which is the case in our work.
Covered by the scientific journal Physical examination letters, the experiment was developed by a team from the USTC and the University of Seville to answer a fundamental question: are complex numbers really necessary for the quantum mechanical description of nature? The results rule out an alternative to standard quantum physics that uses only real numbers.
According to Jian-Wei Pan: “Physicists use mathematics to describe nature. In classical physics, a real number seems complete in describing physical reality in any classical phenomenon, whereas a complex number is only sometimes employed as a convenient mathematical tool. However, whether the complex number is necessary to represent quantum mechanical theory remains an open question. Our results refute the real number description of nature and establish the indispensable role of a complex number in quantum mechanics.
“It’s not just interesting to rule out a specific alternative,” adds Cabello, “the importance of the experiment is that it shows how a system of superconducting qubits [those used in quantum computers] allows us to test quantum physics predictions that are impossible to test with the experiments we have conducted so far. This opens up a very interesting field of possibilities, as there are dozens of fascinating predictions that we have never been able to test because they require firm control over multiple qubits. Now we can test them.
According to Chao-Yang Lu, of the USTC and co-author of the experiment: “The most promising short-term application of quantum computers is the testing of quantum mechanics itself and the study of systems with many body”.
Thus, the discovery not only provides a way forward in the development of quantum computers, but also a new way of approaching nature to understand the behavior and interactions of particles at the atomic and subatomic level.
But, like any breakthrough, the opening of a new path generates uncertainties. However, Jian-Wei Pan prefers to focus on the positive: “Building a practically useful and fault-tolerant quantum computer is one of the great challenges for human beings,” he says. “I’m more concerned about how and when we’ll build one. The most formidable challenge to building a large-scale universal quantum computer is the presence of noise and imperfections. We need to use quantum error correction and fault-tolerant operations to overcome the noise and scale the system. A logical qubit with higher fidelity than a physical qubit will be the next breakthrough in quantum computing and will happen in about five years. In homes, quantum computers would, if realized, be available first through cloud services.
According to Cabello, “when quantum computers are big enough and have thousands or millions of qubits, they will allow understanding complex chemical reactions that will help design new drugs and better batteries; perform simulations that lead to the development of new materials and calculations to optimize the artificial intelligence and machine learning algorithms used in logistics, cybersecurity and finance, or even to decipher the codes on which communications security is based current.
“Quantum computers, he adds, use the properties of quantum physics to perform calculations. Unlike the computers we use, in which the basic unit of information is the bit [which can take two values]in a quantum computer, the basic unit is the quantum bit, or qubit, which has an infinite number of states.
Cabello goes on to say that “quantum computers built by companies such as Google, IBM or Rigetti take advantage of the fact that micron-sized objects produced using standard semiconductor manufacturing techniques can behave like qubits”.
The goal of having computers with millions of qubits is still a long way off, as most of today’s quantum computers, according to Cabello, “only have a few qubits and not all of them are good enough.” However, the results of the research of the Chinese and Spanish team make it possible to broaden the uses of existing computers and to understand physical phenomena that have intrigued scientists for years.
crystal of time
For example, Google Quantum AI published the observation of a time crystal through the Sycamore quantum processor for the first time in the world. Nature newspaper. A quantum time crystal is similar to a grain of salt made up of sodium and chlorine atoms. However, while the layers of atoms in this grain of salt form a physical structure based on repeating patterns in space, in the time crystal the structure is configured from an oscillating pattern. Google’s processor was able to observe these oscillatory wave patterns of stable time crystals.
This discovery, according to Pedram Roushan and Kostyantyn Kechedzhi, shows “how quantum processors can be used to study new physical phenomena. Moving from theory to actual observation is a critical leap and forms the basis of all scientific discovery. Research like this opens the door to many more experiments, not only in physics, but hopefully inspires future quantum applications in many other fields.
In Spain, a consortium of seven companies – Amatech, BBVA bank, DAS Photonics, GMV, Multiverse computing, Qilimanjaro Quantum Tech and Repsol – and five research centers – Barcelona Supercomputing Center (BSC), Spanish National Research Council (CSIC), Donostia International Physics Center (DIPC), Institute of Photonic Sciences (ICFO), Tecnalia and Polytechnic University of Valencia (UPV) – have launched a new project called CUCO to apply quantum computing to strategic Spanish industries: energy, finance , space, defense and logistics.
Subsidized by the Center for the Development of Industrial Technology (CDTI) and with the support of the Ministry of Science and Innovation, the CUCO project, is the first major quantum computing initiative in Spain in the field of business and aims to “advance scientific knowledge and technological knowledge of quantum computing algorithms through public-private collaboration between companies, research centers and universities. The objective is for this technology to be implemented in the medium term.