Quantum computers with their promises of making new materials and solving intractable mathematical problems are a dream of the many physicists. Now, they’re slowly approaching viable realizations in many laboratories everywhere world wide . But there are still enormous challenges to master. A central one is that the construction of stable quantum bits – the fundamental’ unit of quantum computation called qubit for brief — which will be networked together.
In a study published in Nature Materials and led by Daniel Jirovec from the Katsaros group at IST Austria in close collaboration with researchers from the L-NESS Inter-university Centre in Como, Italy, scientists now have created a latest and promising candidate system for reliable qubits.
The researchers created the qubit using the spin of so-called holes. Each hole is simply the absence of an electron in solid material. Amazingly, a missing charged particle can physically be treated as if it were a +ve(positive) charged particle. It can even move around within the solid when a neighboring electron fills hole . Thus, effectively the hole described as +ve charged particle is moving forward.
These holes even carry the quantum-mechanical property of spin and may interact if they come close to one another . “Our colleagues at L-NESS layered several different mixtures of silicon and germanium just a couple of nanometers thick on top of every other. that permits us to confine the holes to the germanium-rich layer in middle,” Jirovec explains. “On top, we added tiny electrical wires — so-called gates — to regulate the movement of holes by applying voltage to them. The electrically charged holes react to the voltage and may be extremely precisely moved around within their layer.”
Using this nano-scale control, the scientists moved two holes close to one another to make a qubit out of their interacting spins. But to create this work, they needed to use a magnetic flux to the entire setup. Here, their innovative approach comes into play.
In their setup, Jirovec and his colleagues cannot only move holes around but also alter their properties. By engineering different hole properties, they created the qubit out of the 2 interacting hole spins using lower than 10 millitesla of magnetic flux strength. this is often a weak magnetic flux compared to other similar qubit setups, which employ a minimum of ten times stronger fields.
But why is that relevant? “By using our layered germanium setup we will reduce the specified magnetic flux strength and thus allow the mixture of our qubit with superconductors, usually inhibited by strong magnetic fields,” Jirovec says. Superconductors – materials with none electric resistance — support the linking of several qubits thanks to their quantum-mechanical nature. this might enable scientists to create new kind of quantum computers combining semiconductors and superconductors.
In addition to the new technical possibilities, these hole spin qubits look promising due to their processing speed. With up to at least one hundred million operations per second also as their long lifetime of up to 150 microseconds they appear particularly viable for quantum computing. Usually, there’s a tradeoff between these properties, but this new design brings both advantages together.
The research published in Nature Journal.