Physicists at the Delft University of Technology, Netherlands, have achieved a milestone that might soon revolutionize the world of quantum computing, quantum physics, and perhaps shed new light on the mystery of the dark matter in our universe. Experimenting with nanoelectronics, a group led by Prof. Leo Kouwenhoven has succeeded in detecting the elusive Majorana fermion in the laboratory, without the need for a particle accelerator.
The find is the culmination of decades of research. First theorized by Italian physicist Ettore Majorana in 1937 by building on the work of Erwin Schrödinger and Paul Dirac, the Majorana fermion emitted too weak a signal to be spotted within most materials. Recently, however, theoretical physicists have suggested that some exotic materials might circumvent defects and impurities found elsewhere and allow for the detection of this elusive particle.
Building on this knowledge, Kouwenhoven connected indium antimonide nanowires to a circuit with a gold contact at one end and a slice of superconductor at the other, and then exposed the circuit to a moderate magnetic field. Measurements of the electrical conductance of the nanowires showed a peak at zero voltage that is consistent with the formation of a pair of Majorana particles.
This special kind of fermion has the unique property of being its own antiparticle. An antiparticle is defined as a subatomic particle having the same mass as a given particle, but opposite electric or magnetic properties – for instance, the antiparticle of a negatively-charged electron is a positively-charged positron. The unique properties of Majorana fermions generate an interesting behavior whenever two particles interact.
Elementary particles come in two kinds: bosons, such as photons, and fermions, such as electrons. Besides having different charge and spin properties, they also behave quite differently when two particles of the same kind interact with each other.
When two bosons trade places, there is no change in their quantum mechanical state, and they become interchangeable; when two normal fermions trade places, the sign of their mathematical "wavefunction" changes from positive to negative with each switch, returning to their original state after two switches. Majorana fermions, on other hand, "remember" their previously taken path.
This property makes Majorana fermions a very strong candidate for use in quantum computers. While we've seen a number of developments in quantum computing in recent years, from qubits in semiconductors to manipulating quantum information through electrical fields, one longstanding issue is that the qubits – "quantum bits," the basic unit of information in a quantum computer – are unstable and highly sensitive to external influences.
Not so with this particle, which promises to be unaffected by external influences (even though, it should be pointed out, it’s not yet entirely clear whether qubits created in this manner will be long-lived enough to be used in that way).
More broadly, the "memory" of these particles could be a crucial factor that will enable researchers to more effectively crack some of the long-standing mysteries of quantum mechanics once and for all, helping to investigate the behavior of other particles.
Also, as some researchers suggest, the particles may play a crucial role in cosmology – a proposed theory assumes that the mysterious dark matter, which is thought to form around 73 percent of our Universe, is composed entirely of Majorana fermions.
The video below illustrates the process by which Kouwenhoven's team managed to isolate the fermions.
The research was published in the journal Science and was financed by the FOM Foundation and Microsoft.