Computers are becoming faster and more energy-efficient, yet there is a limit to what state-of-the-art technology can do. Researchers have therefore begun working with quantum computers, which are super-fast and highly efficient. Physicist Henk Stoof 's research is at the base of this innovation. "As a theorist, I am good at establishing connections between the various fundamental scientific disciplines."
Electricity can travel from an electrical outlet to a lamp because a power cord connects the two. Henk Stoof switches on his desk lamp and grabs hold of the power cord that connects the lamp to the electrical outlet. "Power cords such as this one often have an insulated copper wire, which conducts current," he explains. "However, a lot of energy is lost in the copper wire: nearly a third of electrical energy is converted into heat. A superconductive material ensures that an electrical charge can travel without resistance and without suffering from a loss of energy. It is much more sustainable." Physicists only face one problem: superconductivity can currently only be achieved in materials that have to be cooled to far below the freezing point of water.
Stoof switches off the light. "We recently demonstrated that superconductivity at much higher temperatures is also possible, albeit with the help of ultra-cold atom clouds of -273℃. We call this result a proof of principle. We want to transfer these superconductive features to metals at room temperature, so that we can also achieve superconductivity in wires from an electrical outlet to a lamp."
Small quantum computers have been used in labs for quite some time. However, as Stoof indicated, this is a proof of principle. It works, but it is not yet fully applicable in society. Quantum computers still have to be cooled to extremely low temperatures to be able to function, and that takes a lot of energy. Moreover, they are much too small at the moment and can only handle simple calculations.
Spin up, spin down
Superconductivity is not the only thing on Stoof's agenda. "Together with Rembert Duine, I also conduct research into so-called topological insulators," says Stoof.
"That means that a material only conducts electricity on the outside, but insulates on the inside. It is currently a hot topic in the world of physics, and we think that this could be used in quantum computers in the future."
A topological insulator has rare quantum-mechanical features. Current transfer is in fact nothing more than the movement of electrons (negatively charged particles). The electrons can revolve around their axis and therefore have a magnetic field around them which can have two directions: up or down. This is also known as the electron spin. If the direction of the magnetic field is upward, this is called spin up; if it is downward, it is called spin down. The unique feature of a topological insulator is that electrons that move in one direction have a spin up and those that move in the opposite direction have a down spin. There is a very special relationship between the movement of the electron and its spin.
"Making use of the spin of electrons in electrical devices is called spintronics,” explains Stoof. "This seems like science fiction, but it really is not. Computer hard disks already use it. Data on hard drives is stored as ones and zeros. The magnetic field of a part of a computer hard disk either points up or down, and this can be read with the help of electric current due to the electron spin."
"My work is mostly focused on fundamentals," says Stoof. "A theorist such as myself can establish connections between various fundamental scientific disciplines, as a mathematical model can apply to more than one system. This allows me to stand at the base of experimental developments and I try to gear my research towards that."