After TU Delft researchers had to retract their Nature publication about a promising building block for future quantum computers two years ago, they are now coming up with a new approach. Taking a step back, the coveted stable Majorana particles are within sight.
Delft researchers led by Leo Koenhoven have been searching for Majorana particles for more than a decade. In 2012, they found the first signs of hope. Majorana particles are not elementary particles, like electrons, but they are called Quasiparticleswhere the particles in a substance collectively behave as if they were particles.
Majorana particles
Substances in which these macroparticles are excited can protect them from external disturbances. This stability makes Majorana on paper very suitable as building blocks for a future quantum computer, which can perform certain tasks much faster than is possible with current computers.
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A publication in Nature in 2018 showed that Delft researchers had succeeded in finding Maurana particles at the ends of super-thin, superconducting nanowires. But after criticizing the measurements, they had to withdraw this article in 2020.
Since then, the research group has not been idle. They are working on a new approach Now he succeeded It seems to make simpler, “Grand Austerity.” This is the first step towards more stable Majorana particles.
“In recent years,” he says, ”it has become apparent that with careful measurements, you can see phenomena arising in your matter which at first appears very similar to Majorana, but which does not have all the necessary properties. Guanzhong WangPhD candidate at QuTech, Research Institute for Quantum Technology at TU Delft and TNO.
short series
This raised the question of why the nanowires did not behave as hoped. Delft researchers believe that the substances are not pure enough, which is causing disturbances. In theory, the Majorana should be able to withstand such disturbances, but there is a limit to that. Looks like there was a lot of turmoil.
That’s why researchers have now taken a step back. They made a shorter, simpler nanowire, with which they could better control the conditions. Majorana particles always appear in pairs, one at the end of each nanowire. You can think of a Majorana pair as two half electrons.
The shorter nanowire is somewhat reminiscent of a string of beads, because it consists of so-called quantum dots, which are tiny islands of Semiconductors In a non-conductive environment, with a piece of nanowire covered with a superconducting material between them. Electrons can move back and forth between the quantum dots and the superconducting piece of nanowire in specific ways. “By controlling very precisely the behavior of the electrons in the superconducting part, we can ensure that majoranas form at the ends,” he says. Tom Dvira postdoctoral researcher at QuTech.
The researchers have now shown that they have enough control over the simplified system with two quantum points to allow the emergence of simple “sober Majoranas”.
gum
“The next step is not only to measure the Majorana particles, but also to manipulate them so that we can use them as qubits,” Dvir says. “At the same time, we’ll see if we can make the chain longer, so that the Majorana mountains are more spaced apart, which makes them more stable and robust.”
“I think it’s a cool experiment,” says the theoretical physicist. Carlo Benacer from Leiden University, who was not involved in the research. They take a step back first to build something they understand well, and then carefully, step by step, to work toward the ultimate goal: a stable Majorana.
The two big Bennakers compare their ending to a piece of chewing gum unraveling. If you take it apart until it breaks into two pieces, you have two principal particles. If you put them back together, you’ll get your old electron back.
The first step
“Now what they’ve done in the experiment is separate the gum a little bit,” Benaker says. But the parts are inseparable from each other. So they can go straight back to the electron.
So Benaker sees it as a first step towards a “true Majorana particle”. “Maybe if you made a longer string and pulled harder, you’d get two independent particles, but we’re not there yet.”
