Last month, Microsoft introduced a new quantum computing chip known as Majorana 1 that it anticipated would “realise quantum computers capable of solving meaningful, industrial-scale problems in years, not decades”. Independent scientists quickly raised doubts about this declare — grandiose as it’s — but in addition acknowledged Microsoft had taken on an incredible problem to construct such a chip and that its efforts on this route couldn’t or shouldn’t be written off altogether.
Microsoft named the chip “Majorana 1” as a result of it consists of Majorana particles, which is a specific sort of subatomic particle with uncommon properties. One is {that a} Majorana particle is its personal anti-particle. The particles that make up matter, known as fermions, have anti-particles with distinct identities. For instance, the electron’s anti-particle is a positron, not one other electron. The proton’s anti-particle is the anti-proton, not one other proton. But uniquely amongst fermions, a Majorana particle’s anti-particle is one more Majorana particle. If two of them meet, they are going to annihilate one another in a flash of vitality.
One of the most important open questions in modern physics is whether or not neutrinos are Majorana particles.
Neutrinos, neutrinos all over the place
Neutrinos are the second-most considerable subatomic particle within the universe, after photons, the particles of sunshine. They have been produced in copious quantities through the Big Bang occasion. They are produced in radioactive decay, when huge stars explode, and when cosmic rays strike the earth’s environment. They are additionally made throughout nuclear fusion: the solar alone is accountable for flooding each sq. centimetre on the earth with 60 billion neutrinos every second. These particles are additionally terribly arduous to catch as a result of they work together very weakly and really hardly ever with matter.
Yet it’s essential physicists research them: neutrinos may be the important thing to answering most of the open questions on our universe. Their large numbers are an indication that they’re concerned in lots of, many subatomic processes. Thus a transparent view of their properties may also afford physicists a transparent view of those processes, and the as-yet unresolved questions they will reply.
We don’t know many issues about neutrinos. Perhaps the largest unknown is how a lot a neutrino weighs. We know neutrinos are available three flavours, or varieties, and we all know the variations between the squares of their lots, however not the person lots themselves. If neutrinos are discovered to be Majorana particles, the process that reveals them to be could be simply used to reveal their lots as nicely. This process is known as neutrinoless double beta decay, or 0vßß for quick.
Chilling with beta decay
Every atom has some vitality, which it bears in its particles and the forces performing between them. Sometimes an atom’s nucleus could have an excessive amount of vitality, rendering it unstable and searching for alternatives to shed the surplus. This notion of stability comes from the truth that for each set of protons and neutrons within the nucleus, there’s a quantity that enables the particles to organize themselves in a means that leaves the nucleus with the naked minimal of vitality.
For instance, the nucleus of the actinium-227 atom accommodates 89 protons and 138 neutrons, forcing the nucleus to exist in a extremely unstable configuration. To shed the ‘excess energy’, it undergoes a process known as beta decay: it emits an electron and an anti-neutrino and adjustments to the thorium-227 nucleus. Th-227 additionally isn’t steady and decays additional, however because the beta decay process releases vitality, the nucleus is healthier off than it was earlier than.
In nature, beta decay is a standard means for an unstable nucleus to decay. It can occur in considered one of two kinds relying on whether or not a nucleus has too many neutrons or too many protons. In the primary case, a neutron is transformed to a proton and releases an electron and an anti-neutrino. In the second, a proton is transformed to a neutron and releases a positron and a neutrino. A 3rd type exists the place two beta decays occur concurrently, i.e. two neutrons are concurrently transformed to two protons, emitting two electrons and two anti-neutrinos.
The conversion skill stems from the weak interplay, which is among the 4 methods during which subatomic particles can work together with one another. (The others are the sturdy, electromagnetic, and gravitational interactions.) The weak interplay is characterised by the looks of particles known as W or Z bosons. For instance, through the Ac-227 beta decay, a neutron emits a W– boson and turns right into a proton, and the W– boson decays to an electron and an anti-neutrino.
An indication within the distinction
As widespread as beta decay is, scientists are at present on the hunt for a particularly uncommon variant: 0vßß. It could not even exist, however simply in case it does, it might show neutrinos are Majorana particles.
In 0vßß, a nucleus emits two electrons as an alternative of an electron and an anti-neutrino. This can occur solely when the neutrino emitted by one neutron is absorbed as an anti-neutrino by the opposite neutron, which in flip can solely occur if neutrinos and anti-neutrinos are the identical factor. Each of the emitted electrons additionally has extra vitality as a result of it ‘includes’ the vitality of the lacking anti-neutrino. Experiments trying for proof of 0vßß can thus use this vitality distinction to inform whether or not a nucleus has undergone beta decay or 0vßß.
This is exactly what the AMoRE experiment in South Korea has been doing, with delicate particle detectors pointed at a crystal containing 3 kg of molybdenum-100 nuclei, cooled to fractions above absolute zero. Mo-100 nuclei are identified to bear double beta decay.
The search continues
In a paper revealed in Physical Review Letters on February 27, the AMoRE group reported it hadn’t noticed proof of 0vßß. Because the process is already hypothesised to be uncommon, not observing it may simply as simply imply we didn’t look lengthy sufficient. This is why the group reported within the paper {that a} inhabitants of Mo-100 nuclei would decay to half their quantity by means of 0vßß in at least 1024 years. It may additionally imply 0vßß would possibly present itself in a bigger pattern. In a future iteration of AMoRE, the physicists plan to look for it in 100 kg of Mo-100.
Meanwhile, they’ve additionally estimated the mass of every neutrino would have to be decrease than 0.22-0.65 billionths of a proton. This is a particularly low mass ceiling, nevertheless it’s not the identical as saying the neutrinos have zero mass. The distinction is essential. The present idea of all subatomic particles, known as the Standard Model of particle physics, says neutrinos needs to be massless. The presence of even a small quantity of mass thus vexes the idea and signifies it has a spot someplace. The hassle is physicists don’t but know the place. So AMoRE appears to be like ahead to its upgraded type and the search continues.
Published – March 18, 2025 05:30 am IST
