If you thought the search for the Higgs boson - the elusive particle that endows matter with mass - was epic, spare a thought for the physicists who have been trying to find a way to discover another subatomic particle that has remained hidden since it was first theorized in the 1930s.
But now, through the use of a two-story-tall microscope, the very strange and (potentially) revolutionary particle has been tracked down.
Introducing the Majorana fermion: a particle that is also its own antiparticle, dark matter candidate and possible quantum computer enabler.
The Majorana fermion is named after the Italian physicist who formulated the theoretical framework that described this unique particle, Ettore Majorana. In 1937, Majorana predicted that a stable particle could exist in nature that was both matter and antimatter. In our everyday experience, there is matter (which is abundant in our known universe) and antimatter (which is very rare). Should matter and antimatter meet, they both annihilate, disappearing in a flash of energy.
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One of the biggest conundrums in modern physics is how the universe became more matter than antimatter. Logic suggests that matter and antimatter are one in the same thing, like the opposite sides of the same coin, and should have been created at the same rate. In this case, the universe would have annihilated before it could have even gained a foothold. But some process after the Big Bang ensured that more matter than antimatter was produced, so matter won out to create the matter-filled universe we know and love today.
However, the Majorana is different; it is its own antiparticle. Whereas an electron is matter and the positron is the electron's antimatter particle, for example, the Majorana is both matter and antimatter -- at the same time. It is this matter/antimatter duality that has made this little beastie so hard to track down for the past eight decades.
But track it down physicists did and it took some stunning ingenuity and a whopping great microscope to accomplish the task.
Theory suggests that the Majorana should emerge at the edge of other materials. So the Princeton team constructed an atom-thick iron wire on a lead surface and zoomed in on the end of that wire with the mega-microscope at the ultralow-vibration laboratory at Princeton's Jadwin Hall.
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"This is the most direct way of looking for the Majorana fermion as it is expected to emerge at the edge of certain materials," said lead physicist Ali Yazdani of Princeton University, N.J., in a press release. "If you want to find this particle within a material you have to use such a microscope, which allows you to see where it actually is."
Yazdani's research was published in the journal Science on Thursday (Oct. 2).
The search for the Majorana is very different from searches for other subatomic particles that have seen much mainstream press. The hunt for the Higgs boson (and particles like it) need the most powerful accelerators on the planet to generate the vast collisional energies required to simulate the conditions soon after the Big Bang. This is the only way to isolate a rapidly-decaying Higgs boson and then study its decay products that betray its existence.
In contrast, the Majorana can only be detected in a material by its effect on the atoms and forces surrounding it - so no powerful accelerators are required, but powerful scanning-tunneling microscopes are a must. Also, very fine controls on the target material is required so the Majorana can be isolated and imaged.
This stringent control required extreme cooling of the thin iron wire to ensure superconductivity. Superconductivity is attained when the thermal vibrations in a material are lowered to such an extent that electrons can pass through that material with zero resistance. By lowering the target to -272 degrees Celsius - just one degree above absolute zero, or 1 Kelvin - the perfect conditions for Majorana formation could be attained.
"It shows that this (Majorana) signal lives only at the edge," Yazdani said. "That is the key signature. If you don't have that, then this signal can exist for many other reasons."
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Previous experiments have picked up possible Majorana signals in similar setups, but this is the first time that a definite signal - after all other sources of interference have been removed - of a Majorana fermion at the location it was predicted to be. This could only be achieved by keeping the experimental setup simple and not using exotic materials that could introduce noise, argues Yazdani.
"What's very exciting is that it is very simple: it is lead and iron," he said.
From Dark Matter to Quantum Computing
Now it has been discovered, there are some exciting implications for several areas of modern physics, engineering and astrophysics.
For example, the Majorana is extremely weakly interacting with normal matter, much like the ghostly neutrino. Physicists are not sure whether the neutrino has a separate antiparticle or whether, like the Majorana fermion, is its own antiparticle. Neutrinos are abundant in the universe and astronomers often point to neutrinos being a significant portion of dark matter that is thought to fill the cosmos. Perhaps neutrinos are also Majorana-like particles and Majorana fermions are also a dark matter candidate.
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There is also a potentially revolutionary industrial application should physicists be able to encode matter with Majorana fermions. Currently, electrons are being used in the quantum computing effort, potentially creating computers that can solve previously incalculable systems in an instant. But electrons (also a fermion) are notoriously difficult to control, often collapsing calculations after interacting with other materials surrounding them.
The Majorana fermion, however, is extremely weakly interacting with matter due to its matter/antimatter duality and is surprisingly stable. It is for these reasons that scientists may be able to harness the Majorana, engineering it into materials, encoding it and potentially opening up new and novel quantum computing applications.
So although its discovery may not have the drama and action of smashing relativistic particles together in the vacuum chambers of the LHC's building-sized detectors, the more subtle Majorana discovery could develop a new understanding for dark matter and aid a revolution in computing.
That 80-year wait for its discovery was probably worth it after all.
Source: Phys.org/Princeton University