Write your abstract here.Photon-
transistors for the supercomputers of the future. August 26th, 2007.
Scientist
from the Niels Bohr Institute at University of Copenhagen and
from Harvard University have worked out a new theory which describe how
the necessary
transistors for the
quantum computers of the future may
be created. The research has just been published in the scientific
journal Nature Physics.
Researchers dream of quantum computers. Incredibly fast super
computers which can solve such extremely complicated tasks that it will
revolutionise the application possibilities. But there are some serious
difficulties. One of them is the transistors, which are the systems
that process the signals.
Caption: Two
photons are sent through a nanowire towards an atom, where they
collide, such that one photon (red) transfers its information to the
other photon. Credit: Anders Søndberg Sørensen, associate professor,
University of Copenhagen
Today the signal is an electrical current. For a quantum computer
the signal can be an optical one, and it works using a single photon
which is the smallest component of light.
“To work, the photons have to meet and “talk”, and the photons very
rarely interact together” says Anders Søndberg Sørensen who is a
Quantum Physicist at the Niels Bohr Institute at Copenhagen University.
He explains that light does not function like in Star Wars, where the
people fight with light sabres and can cross swords with the light.
That is pure fiction and can’t happen.
When two rays of light meet and cross, the two lights go right
through each other. That is called linear optics.What he wants to do
with the light is non-linear optics. That means that the photons in the
light collide with each other and can affect each other. This is very
difficult to do in practice. Photons are so small that one could never
hit one with the other. Unless one can control them – and it is this
Anders Sørensen has developed a theory about.nstead of shooting two
photons at each other from different directions and trying to get them
to hit each other, he wants to use an atom as an intermediary. The atom
can only absorb one photon (such are the laws of physics). If you now
direct two photons towards the atom it happens that they will collide
on the atom. It is exactly what he wants.
The atom is however very small and difficult to hit. So the photons
have to be focussed very precisely. In a previous experiment
researchers had discovered that microwaves could be focussed on an atom
via a superconducting nano-wire. They got the idea that the same could
happen with visible light.The theoretical model shows that it works.
The atom is brought close to the nanowire. Two photons are sent towards
the atom and when they hit it an interaction occurs between them, where
one imparts information to the other.
The information is sent in bits which are either a one or zero
digit, and the order of digits produces the message. (Today we can send
information via an optic cable and each bit is made up of millions of
photons.) In quantum optics each bit is just one photon. The photon has
now received its message and the signal continues on its way. It is a
step on the way to building a photon-transistor for a quantum computer.
Source: University of Copenhagen