Particles that are their own enemies – A proposed device could lead to observation of particles that are their own antiparticles

The matter that makes up the universe consists of particles such as
electrons and protons, as well as their counterparts known as
antiparticles. Particles and antiparticles that collide, however,
annihilate each other in an intense flash of energy. Nevertheless,
the Italian physicist Ettore Majorana proposed that some particles
could exist that are their own antiparticles although physicists are
yet to observe such particles.
Researchers from the RIKEN Advanced Science Institute in Wako
have now proposed a scheme where Majorana particles could be
not only observed for the first time but also manipulated1. The
observation would occur in a conventional material rather than
space. “Our main aim is to find a platform where the existence
of Majorana fermions can be shown,” explains team member
Shigeki Onoda. “And beyond that, we propose concrete steps
towards the control of several Majorana particles.”
In some rare materials, energetic excitations that resemble Majorana
particles are predicted to exist in materials. One class of these
materials is known as topological insulators on the surface of
which electrons can travel almost unperturbed. In topological
insulators that are also superconducting, Majorana particles are
predicted to exist in the presence of magnetic fields. These
Majorana particles can be imagined as electronic excitations
that run around the magnetic field lines.

Figure 1: A schematic diagram of Majorana particles lined up in
two opposing magnetic fields (red) that interact with a superconducting
topological insulator (blue). At the gap between the magnets, the
superconductor is weakened and magnetic field lines assemble in
a periodic chain to which Majorana particles (yellow) attach


The device proposed by Onoda and his colleagues offers deliberate
control over Majorana particles within a topological insulator that
they hope will make them accessible to experiments. Their device
consists of a surface of a superconducting topological insulator
attached to two magnetic sections (Fig. 1). The magnetic fields
of the two magnets point in opposite directions. The researchers
predict that, along the interface between the magnets, a periodic
chain of magnetic field lines form in the superconducting
topological insulator. Each of these magnetic field lines could
accommodate a Majorana particle.

Once their existence is proved, Majorana particles could also enable
extremely stable new forms of computing based on quantum physics,
says Onoda. “As long as the Majorana particles are well separated,
the information encoded in these states would be robust against
local perturbations.”

For the time being, however, such quantum computing schemes
must remain theoretical. Although widely expected to exist,
superconducting topological insulators, as yet, exist only in
theory. Once such a material has been found, the researchers
believe that the proposed device structure will be straightforward
to implement. The expected periodic arrangement of Majorana
particles would then provide a convenient platform to study
these elusive particles.