Re: Could we theoretically use photons instead of electrons in a processor?

Greetings Daniel:

Yes we can theoretically use photons in place of electrons for data processing;
however, there are many difficult problems that must be overcome
before photonic circuits can compete with today's electronic circuits.

Electrons are in the class of fundamental particles called Leptons which
have a spin = 1/2. Electrons have a mass and a charge = -1. Photons are
in the class of fundamental particles called Bosons which have a spin = 1.
Photons have no mass or charge and they are not affected by magnetic
fields. To exist photons must travel at the speed of light within the
medium they are passing through. Electrons can be at rest or they can
move at great velocities; however, because they have mass, electrons
cannot reach the speed of light because the Theory of Relativity teaches
that at that velocity their mass would become infinite. Because of their
negative charge electrons repel each other and they are attracted to
positive charges. Magnetic fields can bend the path of a moving electron.
Photons can pass through one another without interacting and they are not
affected by charges. For example two beams of photons from a flashlight
or a laser can pass through each other without interacting. Two beams of
electrons will spread apart and bend away from each other. You can
explore the properties of the fundamental particles and forces on the
excellent Particle Adventure web site:

http://par ticleadventure.org/particleadventure/index.html

Because of the greater velocity of photons and their potential for greater
bandwidths, as demonstrated by fiberoptic systems, it would seem that
photonic computers would have a speed advantage over electronic computers;
however, to date this has not been demonstrated in small enough devices
for practical applications.

The modern world of electronics is based on controlling the movement of
electrons by varying charged electrical fields and/or changing magnetic
fields. Because they must always be in motion and they are not influenced
by electrical or magnetic fields we must use other methods to control the
behavior of photons. The most developed method to control photons has
been to control the refractive index of the material that the photons
are passing through. This is accomplished by applying electrical, magnetic
and/or acoustic (sound) fields to the
medium which can be a solid, a liquid or a gas. By changing the refractive
index, which is a measure of the speed of light in a material, we can
change the velocity of beams of photons so that they can interfere with
one another and cancel each other or add to each other. This can be
demonstrated in a technique called interferometry. Thus we can use
electrical fields, magnetic fields or pressure fields to control the
amplitude, frequency or phase of a beam of photons and produce amplitude
modulation (AM), phase modulation (PM) or frequency modulation (FM).
However, this control is indirect, we are first changing the properties
of a material, which in turn controls the velocity of the photons. An
electron can directly affect an electron but a photon cannot directly
affect a photon. Never the less logic functions can be demonstrated using
inteferometric techniques. You can see an animated demonstration of
optical interference on the following web site:

http://micro.magnet.fsu.edu/primer/java/doubleslitwavefronts/index.html

Interferometric effects are based on the wavelength of the photonic beam
which typically is between 0.6 micrometers to 1.5 micrometers in fiberoptic
based systems because optical fibers are most transparent in this region
of the electromagnetic spectrum. The smallest inteferometric devices are
called integrated optics and they are formed by using technologies similar
to those used to fabricate integrated electronic circuits. Unfortunately
these devices are typically 5 to 10 millimeters long and about 2
millimeters wide to produce satisfactory switching of a photonic beam
on or off. This is much to large when compared to electronic switches
which are now approaching nanometer dimensions (a nanometer is one
million times smaller than a millimeter).

A proposed holographic memory that uses interferometric effects is
discussed on the following web site; however, you will notice that
currently the equipment used in these experiments would fill a laboratory
bench. Perhaps this can be integrated into a practical size in the future.

http://howstuffworks.lycoszone.com/holographic-memory.htm

At the quantum mechanical level photons have some very strange and
interesting properties. One of these techniques is called quantum
entanglement in which two photons that are created entangled will follow
the quantum state of the other photon no matter how far apart they are separated in space.
This technique has great interest for use in quantum computing and secure
coded communications links. You can read an article "Photons enlisted in
quantum computer search", by R. Colin Johnson, in the March 24,2003
issue of in EE Times on the following web site:

http://www.eetimes .com/at/c/news/OEG20030324S0052


Best regards, Your Mad Scientist
Adrian Popa