Physicists discover behavior of quantum superconductors that offers new level of control

A new study has revealed important behavior in the flow of electrical current through quantum superconductors, which could potentially advance the development of future technologies like quantum computing.

In an article accepted for publication in Physical Examination LettersThe research focuses on Floquet Majorana fermions and their role in a phenomenon called the Josephson effect, which could enable more precise control of quantum computing systems.

The study is co-authored by Babak Seradjeh, professor of physics in the College of Arts and Sciences at Indiana University Bloomington, with theoretical physicists Rekha Kumari and Arijit Kundu of the Indian Institute of Technology Kanpur . It is available on the arXiv preprint server.

Potentially revolutionizing quantum computing

Professor Babak and his colleagues today addressed a central problem in quantum computers: instability. This instability is mainly due to something called quantum decoherence, in which quantum bits, called qubits, lose their delicate quantum state due to interference from their environment, such as temperature fluctuations or electromagnetic noise.

Quantum computers often require the use of superconductors, made from materials that can conduct electricity with zero resistance, meaning they can carry electric current without losing energy. However, current superconductors only operate at extremely low temperatures, close to absolute zero.

This makes quantum computers incredibly power-intensive to stay cold, and therefore stable, because when qubits aren’t cold enough, they become even more unstable, meaning errors happen faster and more frequently.

The scientific pursuit of “room temperature superconductors” is often referred to as the holy grail of superconductivity, due to the very expensive and complex cooling process. If scientists could develop materials exhibiting superconductivity at room temperature (around 20 to 25°C or 68 to 77°F), it could revolutionize technology as we know it, leading to lossless power transmission, at a exponentially faster and more energy efficient electronics. powerful magnets for applications such as MRI machines and advanced energy storage systems.

What makes Floquet Majorana fermions special for quantum computing?

At the heart of the researchers’ study are Majorana fermions, subatomic particles that behave in unique ways; Unlike most particles, Majorana fermions are their own antiparticles. (For every type of particle in the universe, such as electrons and protons, there is a corresponding antiparticle with opposite properties, and this symmetry between particles and antiparticles is a fundamental part of the structure of the universe.)

Researchers postulate that Majorana fermions exist in certain materials, such as topological superconductors. These differ from ordinary superconductors in that a topological superconductor has unique, stable quantum states on its surface or edges that are protected by the underlying topology of the material – the way its structure is shaped at the quantum level. .

These surface states make them resistant to disruption, which explains why they have potential for developing more stable quantum computers. These special edge states can also host exotic particles like Majorana fermions, which do not exist in classical superconductors.

The researchers explored Majorana fermions in a specific context: superconductors that are periodically driven, meaning they are exposed to external energy sources that repeatedly turn on and off. This periodic training modifies the behavior of the Majorana fermions, transforming them into Floquet Majorana fermions (FMF).

Floquet Majorana fermions can exist in distinct states, changing depending on their interaction with the cyclic energy source. These FMFs influence electric current in unique ways, leading to what scientists call the Josephson effect, a quantum phenomenon in which current can flow between two superconductors without the need for an applied voltage, i.e. the pressure that pushes electricity between two points. This periodic control of the superconductor is essential to maintaining FMFs and the unusual patterns they create.

In most systems, the current between two superconductors repeats at regular intervals. However, with FMFs, a special type of electrical behavior occurs in some advanced superconductors, where the current oscillates at half the normal speed, creating a unique, slower pattern, making the system more stable.

This stability is crucial because it could help improve the performance and reliability of quantum computers, which rely on precise and stable quantum states to process information. In other words, this slower oscillation could make quantum devices more efficient and less vulnerable to disruption, which is a major challenge in quantum computing today.

Regulating the current with new techniques

One of the key findings revealed by Babak and colleagues’ study is that the strength of the Josephson current (the amount of electrical flow) can be adjusted using the chemical potential of superconductors.

Simply put, the chemical potential acts like a dial that adjusts the properties of the material, and researchers found that it can be changed by synchronizing with the frequency of the external energy source that drives the system.

This gives scientists a new level of control over quantum materials and opens possibilities for applications in quantum information processing, where precise manipulation of quantum states is essential. The implications for quantum computing are vast, as the technology relies on manipulating quantum states in a stable and predictable manner.

The discovery that Floquet Majorana fermions have unique properties that can be controlled via external drives could pave the way for building quantum computers that are not only faster, but also more error-resistant.

And Majorana fermions are of particular interest to researchers because they are believed to support fault-tolerant quantum computing, that is, where information can be stored and manipulated without being lost to noise or damage. other disturbances.

Although the study is theoretical, the research team confirmed its results through computer simulations, and these results provide researchers around the world with a roadmap for exploring new controllable properties in quantum systems.