Researchers at UCL led by Dr Ed Romans in the London Centre for Nanotechnology have been awarded funding of almost £1 million from the UK's Engineering and Physical Sciences Research Council (EPSRC) to develop new types of hybrid superconductor-semiconductor devices to search for so-far unobserved particles known as Majorana fermions. Their existence was first proposed in 1937 by Italian physicist Ettore Majorana, who was to tragically disappear himself the following year in very mysterious circumstances. He showed that a modification to the relativistic Dirac equation for conventional spin ½ particles (such as ordinary electrons) could give purely real (as opposed to complex) solutions. Such solutions describe a class of particles that are their own antiparticles - in simple terms their creation operator in quantum theory is equal to their annihilation operator unlike the case for conventional electrons where the charge would change sign.
The search for the Majorana fermion has recently received a huge amount of theoretical and experimental interest with both particle and solid state physicists now racing against one another to see who can get there first. In particle physics many theorists believe that neutrinos could be Majorana fermions and complicated experiments are planned or underway at various major laboratories to try and resolve the matter. In the solid state (which is the approach the UCL team will take) the Majorana fermion is predicted to exist as a low energy excitation in certain systems.
Speaking about the challenges ahead, Dr Romans said, "no-one doubts that Majorana fermions can exist, the difficulty is to realize ultraclean samples with just the right interplay of superconducting and magnetic properties to allow them to be created and unambiguously detected. The huge interest in Majorana fermions goes beyond fundamental curiosity though - there is enormous potential for future quantum information technology applications if devices can be made based on manipulation of Majorana Fermions where a qubit can be stored non-locally in a pair of widely separated Majorana states that would be insensitive to the effect of localised sources of decoherence."
Figure: Two superconducting connections made to a semiconducting InAs nanowire deposited by catalyst-free molecular beam epitaxy (MBE) in the Department of Electrical Engineering at UCL.