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April 20, 2012

Majorana Fermion particle may have been discovered and it could explain Dark Matter and enable quantum computers

Scientists at TU Delft's Kavli Institute and the Foundation for Fundamental Research on Matter (FOM Foundation) have succeeded for the first time in detecting a Majorana particle. In the 1930s, the brilliant Italian physicist Ettore Majorana deduced from quantum theory the possibility of the existence of a very special particle, a particle that is its own anti-particle: the Majorana fermion. That 'Majorana' would be right on the border between matter and anti-matter.

Other researchers believe that more evidence needs to be produced to confirm the results.

Quantum computer and dark matter
Majorana fermions are very interesting – not only because their discovery opens up a new and uncharted chapter of fundamental physics; they may also play a role in cosmology. A proposed theory assumes that the mysterious 'dark matter, which forms the greatest part of the universe, is composed of Majorana fermions. Furthermore, scientists view the particles as fundamental building blocks for the quantum computer. Such a computer is far more powerful than the best supercomputer, but only exists in theory so far. Contrary to an 'ordinary' quantum computer, a quantum computer based on Majorana fermions is exceptionally stable and barely sensitive to external influences.

Nanowire
For the first time, scientists in Leo Kouwenhoven's research group managed to create a nanoscale electronic device in which a pair of Majorana fermions 'appear' at either end of a nanowire. They did this by combining an extremely small nanowire, made by colleagues from Eindhoven University of Technology, with a superconducting material and a strong magnetic field. 'The measurements of the particle at the ends of the nanowire cannot otherwise be explained than through the presence of a pair of Majorana fermions', says Leo Kouwenhoven.

Other say more evidence is needed before the claim of Majorana Fermions can be confimed

Journal Science - Signatures of Majorana Fermions in Hybrid Superconductor-Semiconductor Nanowire Devices

Majorana fermions are particles identical to their own antiparticles. They have been theoretically predicted to exist in topological superconductors. We report electrical measurements on InSb nanowires contacted with one normal (Au) and one superconducting electrode (NbTiN). Gate voltages vary electron density and define a tunnel barrier between normal and superconducting contacts. In the presence of magnetic fields of order 100 mT, we observe bound, mid-gap states at zero bias voltage. These bound states remain fixed to zero bias even when magnetic fields and gate voltages are changed over considerable ranges. Our observations support the hypothesis of Majorana fermions in nanowires coupled to superconductors.

Kouwenhoven’s team hopes to use a scheme called “topological quantum computation” that could evade decoherence at the hardware level by storing quantum information non-locally.






Arxiv - Zero bias conductance peak in Majorana wires made of semiconductor-superconductor hybrid structures

Motivated by a recent experimental report claiming the likely observation of the Majorana mode in a semiconductor-superconductor hybrid structure, we study theoretically the dependence of the zero bias condcutance peak associated with the zero-energy Majorana mode in the topological superconducting phase as a function of temperature, tunnel barrier potential, and a magnetic field tilted from the direction of the wire. We find that higher temperatures and tunnel barriers as well as a large magnetic field in the direction transverse to the wire length could very strongly suppress the zero-bias conductance peak as observed. We also show that a strong magnetic field along the wire could eventually lead to the splitting of the zero bias peak into a doublet.

We point out, however, that at best the observations in Leo Kouwenhoven's research establish only the necessary conditions for the existence of the long-sought emergent Majorana modes in solid state systems. Much more work would be needed, including the observation of similar effects in other semiconductor nanowires with strong spin-orbit coupling (e.g. InAs) and the experimental demonstration of the sufficient conditions for the existence of the Majorana modes involving the observation of the fractional Josephson effect and/or the non-Abelian
braiding, before one can compellingly claim to have discovered the elusive Majorana quasiparticles in solid
state systems.

The JQI/CMTC research group has predicted different ways to observe these particles in semiconductor/superconductor systems. For instance, in a variation on their original 1D nanowire proposals, they showed the surprising result that the Majorana fermions in the wire are not so delicate and would survive even if the strict 1D restrictions were relaxed. In fact, the Majorana fermions can be stable, even in the presence of the imperfections and disorder that often exist in solid state materials. A very recent work5 from the group, which appeared on the condensed matter archive on April 15, provided a detailed theoretical analysis of the Delft data, further enhancing the claim that the elusive Majorana particle may have finally been found in nature.

When asked for comments on this development, Das Sarma said “This is certainly very exciting news, it is not often that a theoretical prediction for something totally new actually works out in the laboratory. One, however, has to be cautious because while this experiment from Delft has provided the likely necessary evidence for the existence of the Majorana, the sufficient conditions are more difficult to achieve and may take more time.”

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