Alejandro González Tudela, Research Fellow at CSIC’s Institute of Fundamental Physics, BBVA Foundation
Those most devoted to quantum physics and its potential for computers have been winning bets for some time. Adán Cabello of the University of Seville has already promised a dinner in Rome because he predicted the recent Nobel Prize a decade ago. On the contrary, the Spanish researcher Miguel Navascués, who lives in Austria, lost 50 euros in hamburgers four years ago because he did not expect to control 50 qubits (a basic element of quantum computing) before 2050. Time has proven 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, a 37-year-old scientific researcher at the CSIC Institute of Fundamental Physics, has decided to open a new door to try to solve it: combining the unprecedented capabilities of metamaterials (structures with unusual properties) with the properties of light quanta. 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 was launched in 2014 has been $20 million.
In conventional arithmetic, the basic unit of information is the bit, which can have two values: 0 and 1. The combinations of these already result in 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 using qubits allows trillions of combinations of bits and thus infinite computational possibilities. As Alberto Casas, researcher at CSIC and author of The Quantum Revolution (Ediciones B, 2022) writes, “a quantum computer with 273 qubits will have more memory than the observable universe has atoms”.
The problem is that this quantum property of superposition is currently elusive and only stable for a short time. Any minimal circumstance of the environment (temperature, electromagnetic noise or vibration) degrades them and makes effective quantum computing impossible by performing large-scale practical calculations in a robust way. This effect is called decoherence.
A recent study published in Nature Physics by scientists from the UK and the Universities of Arizona (USA) and Zhejiang (China) used a programmable 30-qubit superconducting processor and showed that “they can be adapted to work with anyone interact while maintaining coherence for an unprecedented 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 González Tudela is exploring takes a new direction: using metamaterials, designed structures with unusual properties, to create quantum devices with more qubits without increasing the error rate. ‘In these metamaterials,’ explains the researcher, ‘their properties are modulated below wavelength to achieve reactions as exotic as a material that is invisible or that focuses light across borders.’
“The initial hypothesis,” says the CSIC researcher, “is based on the fact that light has very good coherence [preserva fácilmente sus propiedades cuánticas]so the goal is to exploit these very strong responses that materials have to light to improve fidelity.”
advantage and disadvantage
The idea is to take advantage of this ability of light to retain its quantum properties as it interacts very little with the environment. However, the same researcher admits that this property is also a disadvantage: “It’s difficult to manipulate”.
This is where his research on metamaterials comes in, which has progressed over the past two years after designing a network of atoms separated by very short distances that allows the quantum behavior of light to be exploited.
“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 wants to advance the control of light through the use of metamaterials, thus overcoming the disadvantage of the difficult manipulation of particles with a more coherent quantum behavior.
The ultimate goal is for this hardware (physical or material element of computers and computer systems) to solve the problem of scalability, building a quantum computer with a larger number of qubits and fewer errors.
“It is interesting,” comments González Tudela, “to explore alternative paradigms. I’m not saying that my proposal will solve the problem, that it will require the big change or the final platform. At the moment the best implementations are trapped ions in superconducting circuits, but there are also such Photon-based quantum technology. Maybe the big leap forward comes from something that’s not on the radar, or from a mix.”
But this researcher emphasizes the need to open new avenues, like the one that received the Leonardo grant. Alberto Casas agrees, writing: “The future of quantum computing is unknown, but undoubtedly worth exploring.”
This potential value of quantum computing does not lie in solving factorial problems like those raised so far, but in testing the system rather than in a practical application. Not even to answer logistical questions like the best route to connect cities? The greatest hopes for this technology, as González Tudela explains, are “certain physical or chemical problems” in addition to cryptography, which would enable secure communications. “These are questions of many bodies, with many elements that interact with each other and that 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: “It may be that other problems are found that are not yet known and could have a quantum advantage, or that applications are developed that are not currently thought of.”
With that in mind, scientists at Trinity College Dublin have published research in the Journal of Physics Communications, after which they believe they have discovered that brains, consciousness and short-term memory processes exhibit quantum behavior. “Quantum brain processes could explain why we can still outperform supercomputers when it comes to unforeseen circumstances, making decisions or learning something new,” says Christian Kerskens, co-author of the paper and a fellow at the University of Ireland’s Neuroscience Institute. According to the researchers, ‘Confirmation of the results, likely with advanced multidisciplinary approaches, would improve the general understanding of how the brain works and help to find innovative technologies and build even more advanced quantum computers.’
Spain remains in the quantum race not only in basic research but also in technological developments. The Barcelona Supercomputing Center – Centro Nacional de Supercomputación (BSC-CNS) has been selected to become 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 is 12.5 million euros, 50% co-financed by the EU and the Secretary of State for Digitization and Artificial Intelligence (SEDIA). “This new infrastructure, which will integrate quantum computing with MareNostrum 5, will allow us to advance in several academic applications,” says Mateo Valero, director of the BSC-CNS, in a statement 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 by European industry and research in areas such as health, climate change, logistics or Power consumption.
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