Leonardo grant: Metamaterials – a new approach to quantum computing | science and technology

Alejandro González Tudela, researcher at the Institute of Theoretical Physics of the Spanish National Research Council.BBVA Foundation

Scientists working on quantum physics in computing have been making friendly bets for years. Adán Cabello, from the University of Seville (Spain), will soon travel to Rome to collect a decade-old bet (a fancy dinner) with a friend regarding this year’s Nobel Prize winner in physics. But four years ago, Spanish researcher Miguel Navascués lost a bet because he didn’t believe a 50-qubit quantum computer could be built before 2050. It cost him €50 worth of hamburgers. Time has favored optimists, but quantum physics still faces the fundamental challenge of increasing computational capacity while reducing error rates. Alejandro González Tudela, a researcher at the Institute of Theoretical Physics of the Spanish National Research Council (CSIC) in Murcia (Spain), is working on a new approach to the problem. It combines the new capabilities of metamaterials (structures with unusual attributes) with the quantum properties of light. His research program has received $20 million in Leonardo grants from the BBVA Foundation since 2014.

In conventional computing, a bit is the basic unit of information. A bit is binary in the sense that it can only have one of two values: 0 or 1. Combinations of bits can provide computers with extraordinary capabilities, but in quantum computing the basic unit is the bit. quantum, or qubit. It is a quantum system that can have one of two states (0 and 1), or any superposition of these states. Superposition is the ability of a quantum system to be in multiple states at the same time until it is measured. The use of qubits allows trillions of combinations of bits and therefore infinite computational possibilities. According to CSIC researcher Alberto Casas, “A 273-qubit quantum computer will have more memory than there are atoms in the observable universe.”

The problem is that this superposition quantum property is elusive and can only remain stable for a short time. The slightest environmental change (temperature, electromagnetic noise or vibrations) degrades this property and prevents quantum computers from performing practical large-scale calculations efficiently. This effect is known as quantum decoherence.

A recent study published in Natural Physics by British, American and Chinese scientists used a programmable 30-qubit superconducting processor to demonstrate that “quantum information processing applications can be tuned to interact with each other while maintaining coherence for an unprecedented amount of time “. Error correction is also used, but this technique involved overcoming one of the challenges of quantum computing – dramatically increasing the number of qubits.

But González takes an innovative approach to the problem. He uses metamaterials, structures with unusual attributes, to create quantum devices capable of reaching more qubits without increasing error rates. “The properties of these metamaterials,” González said, “are modulated below the wavelength needed to achieve rare responses, like making a material invisible or focusing light beyond its boundaries.”

“The hypothesis,” González said, “is based on the fact that light has very good coherence [it easily preserves its quantum properties]. The objective is therefore to exploit the very strong responses of metamaterials to light in order to improve fidelity.

Advantages and disadvantages

The idea is to take advantage of the ability of light to retain its quantum properties since it interacts very little with the environment. However, the downside of using light is that it is difficult to manipulate, González explains.

González decided to use metamaterials in his research after the recent development of a network of atoms separated by very short distances made it possible to exploit the quantum behavior of light. “By placing the atoms at very short distances, they behave collectively and can have very strong interactions with light,” González said. This will allow him to use metamaterials with more coherent quantum behaviors to overcome the difficulty of manipulating light particles. The ultimate goal is to develop computer hardware that solves the scalability problem – a quantum computer with more qubits and fewer errors.

“It’s interesting,” González said, “to explore alternative paradigms. I’m not saying that my approach will result in the breakthrough that will solve the problem and become the definitive platform. Currently, the best implementations of quantum computing use ions trapped in superconducting circuits, but there is also quantum technology based on photons. Maybe the big leap forward will come from something completely off the radar, or some combination of solutions. Nevertheless, González strongly feels the need to blaze new trails with projects like the one that received the Leonardo grant. Alberto Casas agrees. “The future of quantum computing is unknown, but definitely worth exploring,” he writes in his recently published book, The quantum revolution.

The interest of quantum computing is not to solve factorial calculations like those used to test systems. Nor is it about solving logistical puzzles like the best transport routes between cities. Besides cryptography, González says that the biggest aspirations of this technology are to enable secure communications and to solve “certain problems in physics and chemistry. These are multi-faceted problems with many interacting elements that are difficult to solve using traditional computers.

The pharmaceutical industry is one area where quantum computing can provide an “exponential advantage” in the development of personalized therapies, González says. “Perhaps new problems will be identified that could benefit from quantum computing, or new applications that we haven’t yet imagined will be developed.”

Quantum brains

Scientists from Trinity College Dublin (Ireland) published an article in the Physical Communications Journal which describes the quantum behaviors of the brain, consciousness and short-term memory processes. “Quantum brain processes could explain why we can still outperform supercomputers when it comes to unforeseen circumstances, decision-making and learning new things,” said co-author Christian Kerskens, a physicist at the Institute of neuroscience from Trinity College. According to the study, “if advanced multidisciplinary approaches validate the results of this study, it will improve the general understanding of brain function and lead to innovative technologies to build even more advanced quantum computers.”

Spain is an active competitor in the quantum race, not only in fundamental research but also in technological innovation. The Barcelona Supercomputing Center has been selected by the European High Performance Computing Joint Undertaking (EuroHPC JU) to host and operate its first quantum computers. The new infrastructure will be installed and integrated with the MareNostrum 5 supercomputer, the most powerful computer in Spain and one of the most advanced in Europe. The QuantumSpain program will invest 12.5 million euros in this project, which is co-financed in equal parts by the European Union and the Spanish Secretariat for Digitization and Artificial Intelligence (SEDIA). “This new infrastructure, which will integrate quantum computing into MareNostrum 5, will allow us to advance multiple academic applications,” Mateo Valero, director of the Barcelona Supercomputing Center, said in a statement. The Barcelona facility will connect to a network of supercomputers in Germany, Czechia, France, Italy and Poland to meet the growing demand for quantum computing resources and services from European industry, and to support research in areas such as health, climate change, logistics and energy consumption.

Sherry J. Basler