Normally Chaotic
Along with their electrical charge, electrons transport their own
rotation, know as 'spin', practically 'for free' as an additional
property. "Each individual electron possesses both charge and spin",
explains Prof. Wieck. "In comparison, an ice skater has grace and
rotation, for example - properties which do not necessarily have to
have a direct connection with one another." The spin creates a small
magnetic field. Both this and the electrical charge could be used for
information technology to the extent that the magnetic fields of
electrons in a semiconductor, which are normally directed chaotically
in all directions, could be aligned in the same direction and this
state could be maintained long enough to enable the possibility of IT
processes. Currently, spin is not in use at all in semiconductor
electronics.
Tiny Magnetic Fields
The newly developing "spintronics" is to change all this by means of "spin
polarisation". And the Ruhr University in Bochum is at the forefront
of the worldwide race for the most application-compatible spintronic
components possible. Prof. Wieck's workgroup has for years been
producing the best "quantum dots", in which spin phenomena are
particularly suitable for study and being put into application. "These
quantum dots are shaped something like the top part of a hamburger bun,
but they are three million times smaller, and some five billion times
five billion quantum dots would fit into an actual hamburger bun top",
explains Wieck in describing the tiny dimensions in which the
researchers are experimenting.
Atomic Nuclei Are The Memory
The interesting thing about quantum dots for the researchers is that
each one can be occupied by precisely one electron. Its spin is
aligned in cooperative work with Dortmund-based physicists headed by
Prof. Manfred Bayer by a laser pulse, and is then transferred to the
surrounding nuclei in the quantum dot. These nuclei are then "spin
polarised" and maintain their polarisation for some ten minutes, in
contrast to the 'more forgetful' electrons. This is more than enough
time to calmly conduct operations such as calculating steps or other
normal computer programs. Afterwards, the nucleus polarisation can
easily be read out by a second laser beam, or an additional pulse can
be used to overwrite it or delete it as needed. "This process is
somewhat similar to nuclear MRI, in which the spin of the nuclei in
somatic cells are equally aligned by a strong magnetic field, only
here it is nanoscopic quantum dots and not the human body that are
being measured", according to Wieck. "Their large quantity and packing
density represents a significant step forward for the processing of
information."
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