I’ve been writing a lot about artificial intelligence lately, and I wanted to break that cycle by writing about something that’s been bugging me for a little while now: namely, the controversy over Microsoft’s claim that it has developed a new and improved version of a quantum microprocessor based on the theoretical “Majorana” particle. What is said particle, you ask? I am not a quantum physicist by any means (I don’t even play one on TV) but I believe it is technically known as a fermion — a class of sub-atomic particles that obey certain rules. Protons and electrons are types of fermion, and so are quarks and weirder things like leptons (but not bosons). The main feature of a Majorana particle is that it acts as its own anti-particle. In regular physics, every particle has an anti-particle with the same mass but the opposite charge (except for photons, which are their own anti-particle because their magnetic charge is zero and the opposite of zero is still zero). When a particle and its anti-particle meet, they annihilate each other.
In case you were wondering (as I was), the Majorana particle is named after a brilliant Italian physicist named Ettore Majorana, who was born in 1906 and did ground-breaking work on theoretical physics; Enrico Fermi compared him to Isaac Newton. He correctly predicted the existence of the neutron, which won its discoverer the Nobel Prize, but in 1938, he disappeared mysteriously. Majorana was a public supporter of Italian fascism and a member of the National Fascist Party, but at the time he disappeared the Italian government had started requiring all university professors to swear an oath of loyalty to the Fascist regime in order to keep their jobs. It’s possible he didn’t want to do this and went into hiding but there is no record of anything written by him after his disappearance, and some colleagues suspect he committed suicide.
How does any of this relate to Microsoft’s quantum processor? Great question. When it comes to the nitty-gritty of the particle’s behavior I am completely out of my depth, so I’m going to defer to Wikipedia’s description of how Majorana particles could emerge, and also how they can (theoretically) be used in quantum computing:
In superconducting materials, a quasiparticle can emerge as a Majorana fermion, more commonly referred to as a Bogoliubov quasiparticle in condensed matter physics. Its existence becomes possible because a quasiparticle in a superconductor is its own antiparticle. Majorana fermions can be bound to a defect at zero energy, and then the combined objects are called Majorana bound states. This name is more appropriate than Majorana fermion because the statistics of these objects is no longer fermionic. Instead, they are an example of non-abelian anyons: interchanging them changes the state of the system in a way that depends only on the order in which the exchange was performed. The non-abelian statistics that they possess allows them to be used as a building block for a topological quantum computer.
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