A key breakthrough for quantum technology

The most common particles are electrons and photons, which are understood to be examples of the large families of fermions and bosons, to which all other particles in nature belong. But there is another possible category of particles, the so-called anyons. Anyons are predicted to arise within materials small enough to confine the wavefunction of the electronic state, as they emerge from the collective dance of many interacting electrons.

One of these is called the Majorana zero mode, anyonic cousins ​​of the Majorana fermions proposed by Ettore Majorana in 1937. Majoranas, as these hypothetical anyones are affectionately called, are predicted to exhibit numerous exotic properties, such as simultaneously behaving like a particle and an antiparticle. allowing mutual annihilation, and the ability to hide quantum information encoding it not locally in space. The last property specifically holds the promise of resilient quantum computing.

Since 2010, many research groups have rushed to find Majoranas. Unlike fundamental particles, such as the electron or photon, which exist naturally in a vacuum, Majorana’s anyons must be created within hybrid materials. One of the most promising platforms to perform them is based on hybrid superconductor-semiconductor nanodevices. Over the past decade these devices have been studied in great detail, hoping to unambiguously prove the existence of Majoranas. However, Majoranas are complicated entities, easily overlooked or confused with other quantum states.

In a new article published in Nature, scientists have shed more light on the mystery of Majorana physics. For the first time, two well-established techniques were applied simultaneously to the same device. To their surprise, the researchers found that states observed with one technique (Coulomb spectroscopy), which at first glance are highly suggestive of Majoranas, were not present when looked at from the different perspective offered by the second technique (tunneling spectroscopy). .

The observations are similar to the following metaphorical scenario. In search of the legendary Majorana rock star, you peek through a door (fountain) into a bar. It seems that a concert is taking place. You clearly see a notable rock star on stage, dressed in a Majorana outfit, singing the Majorana song. The bar is packed with Majorana fans who look at him adoringly. However, when you open a large (drain) door at the other end of the bar, fans rush out, including the so-called rock star. As a true artist, the royal Majorana would never do such a thing.

“That’s precisely what makes Majoranas special. Just as true rock stars don’t leave the stage simply when an exit is available, Majorana anyone remains anchored to the side of the nanodevice by virtue of a deep mathematical principle called topological protection. , even when regular electrons are allowed to escape on the opposite side,” the researchers say.

“Our goal was to figure out how to see if there is a Majorana or not. In our experimental conditions, the gates are nothing more than tunnel barriers that electrons enter and exit. There is a drain gate and a source gate. Viewed from Putting the two spectroscopy methodologies together at the same time, our Majorana rock star imposter turns out to be another type of quasi-particle. Don’t get us wrong, these are interesting superconducting quasi-particles, but not Majoranas,” the scientists continue.

The findings highlight the fact that convincing Majorana impostors are everywhere. They can exist in many different types of devices and can fool different measurement strategies individually. Combining two measurement strategies applied to the same device revealed the imposter through an apparent paradox, an approach that could drastically reduce interpretation ambiguities for future experiments. This is a much-needed step to catch the elusive Majorana and eventually start harnessing her power.