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Majorana 1 Chip
Context:
Microsoft announced a quantum computing chip called Majorana 1, which uses Majorana particles, unique subatomic particles that are their own anti-particles, unlike other fermions (e.g., electrons) which have distinct anti-particles (positrons for electrons, anti-protons for protons).
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- The chip was expected to enable quantum computers capable of solving industrial-scale problems within years, though independent scientists have raised doubts about the feasibility of such claims.
- Majorana particles are special because when two meet, they annihilate each other in a burst of energy. Their unique properties have made them a subject of intense research in the realm of quantum computing and theoretical physics.
- One of the central mysteries in modern physics is whether neutrinos — second-most abundant subatomic particle after photons in the universe — are, in fact, Majorana particles.
Neutrinos and Their Importance
- They are produced during processes like the Big Bang, radioactive decay, supernova explosions, and nuclear fusion (e.g., the Sun generates 60 billion neutrinos per square centimetre per second).
- Neutrinos interact very weakly with matter, making them hard to detect.
- Understanding neutrinos is crucial as they are involved in many subatomic processes and can provide answers to open questions in physics.
- One major unknown is the mass of neutrinos. While we know they come in three different flavours and differences in their mass squared, the exact mass is still undetermined.
- If neutrinos are found to be Majorana particles, their mass could potentially be determined through a process called neutrinoless double beta decay (0vßß).
Neutrinoless Double Beta Decay
- Normally, during beta decay, a nucleus emits an electron and an anti-neutrino when a neutron decays into a proton. In the 0vßß process, however, the nucleus emits two electrons instead of an electron and an anti-neutrino.
- This can only happen if the neutrino emitted by one neutron is absorbed as an anti-neutrino by another neutron, implying that the neutrino and the anti-neutrino are identical — a characteristic of Majorana particles.
- The energy signature of the emitted electrons in 0vßß decay would also be different from regular beta decay. The electrons in 0vßß decay would carry more energy, reflecting the energy that would have been released by the missing anti-neutrino.
- Therefore, by measuring this energy difference, scientists could determine whether a nucleus underwent standard beta decay or the rarer 0vßß decay.
The AMoRE Experiment
- The AMoRE experiment in South Korea is looking for evidence of 0vßß using particle detectors aimed at a crystal containing 3 kg of molybdenum-100 nuclei, which are known to undergo double beta decay.
- The nuclei are cooled to temperatures just above absolute zero to detect the rare event of 0vßß.
- In February 2025, AMoRE’s research team published results in Physical Review Letters, reporting no evidence for 0vßß decay.
- Key Findings:
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- The process is theorised to be extremely rare, and not observing it could mean the experiment didn’t run long enough to detect it.
- The researchers suggested that 0vßß could take as long as 10²⁴ years to occur in a sample of Mo-100 nuclei.
- Future experiments will use 100 kg of Mo-100 to increase the chances of detecting 0vßß.
Neutrino Mass Estimates
- The AMoRE team was able to estimate the upper limit on the mass of the neutrino, which must be less than 0.22-0.65 billionths of a proton.
- This is an incredibly small upper mass bound, but it is important to note that this does not imply that neutrinos are massless.
- According to the Standard Model of particle physics, neutrinos are expected to have no mass, so the discovery of even a small mass would indicate a fundamental gap in the model.
The pursuit of understanding Majorana particles, quantum computing, and neutrinos is at the frontier of both physics and technology, with potentially groundbreaking implications for science in the coming years.
