Metamaterials, the new door to quantum computing

Alejandro González Tudela, scientific researcher at the Institute of Fundamental Physics of the CSIC. BBVA Foundation

Those most devoted 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 having predicted the recent Nobel Prize a decade ago.

On the contrary, the Spanish researcher based in Austria, Miguel Navascués, 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 proved the most optimistic , but this science continues to face fundamental challenges: increasing the capacity of computers and reducing errors.

The Murcian Alejandro González Tudela, a scientific researcher at the Institute of Fundamental Physics of the CSIC, at 37 years old, has decided to open a new door to try to solve them:

combine the unprecedented capabilities of metamaterials (engineered structures with unusual characteristics) with the quantum properties of light.

His work has earned him a Leonardo scholarship from the BBVA Foundation, endowed with up to 40,000 euros per project.

The total aid since the creation of the program, in 2014, has been 20 million.

In conventional 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 (

), a quantum system that can be in two states (0 and 1) or in any superposition

from them.

The consequence is that the use of qubits allows for trillions of combinations of bits and therefore infinite computational possibilities.

As Alberto Casas, researcher at the CSIC and author of

(Ediciones B, 2022) writes, “a quantum computer with 273 qubits will have more memory than the observable universe has atoms”.

More information

Fundamental quantum guide by Alberto Casas: “We are alive thanks to the uncertainty principle”

The problem is that this quantum property of superposition is currently elusive and stable only for a short time.

Any minimal circumstance of the environment (temperature, electromagnetic noise or vibration) degrades it and makes effective quantum computing impossible, performing large-scale practical calculations in a robust way.

This effect is known as decoherence.

A recent investigation, published in

by scientists from the United Kingdom and from the universities of Arizona (USA) and Zhejiang (China), has used a programmable superconducting processor with 30 qubits and shown that "they can be adjusted to interact with each other while maintains 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 that González Tudela is investigating goes in a new direction: using metamaterials, designed structures 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 achieve such exotic responses as a material being invisible or focusing light beyond limits".

"The starting hypothesis", according to the CSIC researcher, "is based on the fact that light has a very good coherence [it easily preserves its quantum properties], so the objective is to exploit these very strong responses that materials with the light to improve fidelities”.

Advantage and disadvantage

The idea is to take advantage of this ability of light to maintain 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 manipulate”.

That is where his research on metamaterials comes in, which has advanced in the last two years after the design of 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 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 a more coherent quantum behavior.

The ultimate goal is that this

(physical or material element of computers and computer systems) solves the problem of scalability, the construction of a quantum computer with a greater number of qubits and fewer errors.

“It is interesting”, comments González Tudela, “to explore alternative paradigms.

I am not saying that my proposal is going to be the one that solves the problem, that it supposes the great change or the definitive platform.

Right now the best implementations are trapped ions in superconducting circuits, but there are also

photon-based quantum technology.

Perhaps the big leap forward comes from one thing that is off the radar or from a mix."

But this researcher highlights the need to open new paths such as the one that has obtained the Leonardo scholarship.

Alberto Casas is of the same opinion, who writes: "The future of quantum computing is unknown, but it is undoubtedly worth exploring."

This potential value of quantum computing is not to solve factorial problems like those raised up to now, more to test 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 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 out 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 known right now that could have a quantum advantage or that applications are developed that are not currently thought of."

quantum brains

In this sense, scientists from Trinity College Dublin have published research in the

after which they believe they have discovered that brains, consciousness and short-term memory processes show quantum behavior.

“Quantum brain processes could explain why we can still outperform supercomputers when it comes to unforeseen circumstances, decision making, or learning something new,”

says Christian Kerskens, co-author of the article and member of the Institute of Neuroscience of the Irish university.

According to the researchers, "if the results were confirmed, probably with advanced multidisciplinary approaches, it would improve the general understanding of how the brain works and help 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 form 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 into 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 Secretary of State for Digitization and Artificial Intelligence (SEDIA).

“This new infrastructure, which will integrate quantum computing with MareNostrum 5,

It will allow us to advance in multiple 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 fields such as health, climate change, logistics or energy use.

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