Metamaterials, the new door to quantum computing

Alejandro González Tudela, research scientist at CSIC’s Institute of Fundamental Physics.BBVA Foundation

Those most dedicated to quantum physics and its potential in computing have been winning bets for some time. Adán Cabello, from the University of Seville, has already promised a dinner in Rome for predicting the recent Nobel prize ten years ago. On the contrary, the Spanish researcher based in Austria, Miguel Navascués, lost 50 euros in hamburgers four years ago because he did not plan to control 50 qubits (a basic element of quantum computing) before 2050. Time is running out. is revealed to be the most optimistic, but this science still faces fundamental challenges: increasing the capacity of computers and reducing errors. Alejandro González Tudela, from Murcia, scientific researcher at the Institute of Fundamental Physics of the CSIC, at 37, decided to open a new door to try to solve them: to combine the unprecedented capacities of metamaterials (structures designed with characteristics unusual) with the quantum properties of light. His work earned him a Leonardo grant from the BBVA Foundation, endowed with up to 40,000 euros per project. Total aid since the program’s inception in 2014 has been $20 million.

In classical computing, the basic unit of information is the bit, which can have two values: 0 and 1. The combinations of these already give an extraordinary capacity. But in quantum computing, the fundamental element is the qubit (quantum bit), a quantum system that can be in two states (0 and 1) or in any superposition of them. The consequence is that the use of qubits allows trillions of bit combinations and therefore infinite computational possibilities. According to Alberto Casas, CSIC researcher and author of the quantum revolution (Ediciones B, 2022), “a quantum computer with 273 qubits will have more memory than atoms in the observable universe.”

The problem is that this superposition quantum property is currently elusive and stable only for a short time. Any minimum circumstance of the environment (temperature, electromagnetic noise or vibration) degrades it and makes efficient quantum computation impossible, performing large-scale practical computations in a robust manner. This effect is known as decoherence.

A recent survey, published in Natural Physics by scientists from the UK and the universities of Arizona (USA) and Zhejiang (China), used a 30-qubit programmable superconducting processor and showed that “they can be tuned to interact with each other while maintaining consistency for an unprecedented length of time.” ”. Error correction is also used, but this technique requires addressing one of the challenges of quantum computing: significantly increasing the number of qubits.

The path studied by González Tudela goes in a new direction: using metamaterials, structures designed with unusual properties, to create quantum devices with more qubits without increasing error levels. “In these metamaterials”, explains the researcher, “their properties are modulated below the wavelength to obtain responses as exotic as an invisible material or focusing light beyond the limits”.

“The starting hypothesis”, according to the CSIC researcher, “is based on the fact that the light has a very good coherence [preserva fácilmente sus propiedades cuánticas]the objective is therefore to exploit these very strong responses that the materials must illuminate to improve fidelity.

Advantage and disadvantage

The idea is to take advantage of this ability of light to retain its quantum properties, since it interacts very little with the environment. However, the same researcher admits that this characteristic is, at the same time, a disadvantage: “It is difficult to handle”.

This is where his research on metamaterials comes in, which has advanced in the last two years after designing a network of atoms separated by very short distances to exploit the quantum behavior of light.

“By placing the atoms at very small distances, they behave collectively and can have very strong interactions with light,” explains González Tudela. In this way, the researcher intends to advance in the control of light with the use of metamaterials and thus overcome the disadvantage of the difficult manipulation of particles with more coherent quantum behavior.

The ultimate goal is that Material (physical or hardware element of computers and computer systems) solves the scalability problem, building a quantum computer with more qubits and fewer errors.

“It is interesting”, comments González Tudela, “to explore alternative paradigms. I’m not saying that my proposal is going to be the one that solves the problem, that it supposes the big change or the definitive platform. Currently the best implementations are trapped ions in superconducting circuits, but there are also photon-based quantum technology. Maybe the big leap forward comes from something that’s off the radar or some mix-and-match.

But this researcher highlights the need to open up new paths like the one who won the Leonardo grant. Alberto Casas agrees, writing, “The future of quantum computing is unknown, but definitely worth exploring.”

This potential value of quantum computing is not in solving factorial problems like the ones raised so far, more for testing the system than as a practical application. Not even to answer logistical questions like what is the best route to connect cities? The greatest hopes for this technology are, as González Tudela explains, in addition to cryptography, which would allow secure communication, “certain physical or chemical problems”. “These are many-body questions, with many elements interacting with each other, which are difficult to solve in classical computers,” he comments.

In this sense, the researcher points to the “exponential advantage” that quantum computing will bring to the pharmaceutical industry in the search for personalized therapies. And he adds, “There may be other problems discovered that are not currently known that could have quantum benefit or applications may be developed that are not currently thought of.”

quantum brains

In this sense, scientists from Trinity College Dublin have published research in Physical Communications Journal after which they believe they have discovered that the brain, consciousness, and short-term memory processes exhibit quantum behaviors. “Quantum brain processes could explain why we can still outperform supercomputers when it comes to unforeseen circumstances, decision-making, or learning something new,” explains Christian Kerskens, co-author of the article and member of the Institute of Neuroscience at the University of Ireland. According to the researchers, “if the results were confirmed, probably with advanced multidisciplinary approaches, it would improve the general understanding of brain function and help find innovative technologies and build even more advanced quantum computers.”

Spain remains in the quantum race not only in fundamental research but also in technological developments. The Barcelona Supercomputing Center – Centro Nacional de Supercomputación (BSC-CNS) has been selected to be part of the EU Supercomputing Consortium, the European High Performance Computing Joint Undertaking, to host and operate the first EuroHPC quantum computers. The new infrastructure will be installed and integrated with the MareNostrum 5 supercomputer, the most powerful in Spain and one of the most advanced in Europe. The investment for this part of the QuantumSpain program will be 12.5 million euros, 50% co-financed by the EU and the State Secretariat for Digitization and Artificial Intelligence (SEDIA). “This new infrastructure, which will integrate quantum computing into MareNostrum 5, will allow us to advance in multiple academic applications”, explains Mateo Valero, director of the BSC-CNS in a press release from the institution. The Barcelona facilities will form a network with supercomputers from Germany, the Czech Republic, France, Italy and Poland to meet the growing demand for quantum computing resources and potential new services from industry and research. European Unions in areas such as health, climate change, logistics or energy consumption.

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Sherry J. Basler