QUANTUM PHYSICS FACTS
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Quantum theory


Quantum theory  has revolutionised physics.  Since it burnt onto the scene a little over a century ago, it has overturned the way we think about subatomic particles and the interactions between them.
Now there.s a new quantum revolution brewing - one that. s set 
to give us technology that can perform feats that were once unimaginable.
Experimental quantum computers are already buzzing away in labs 
around the world. And canadian company  D - Wave systems has started the marketing  the D- Wave one, which it describes as ,the world, s first commercially available quantum computer, with a price tag of $10,000,000 ($6.2m). However .some critics have questioned whether it has all  the properties of a full quantum computer.
But it’s not just computers that will
be transformed by harnessing quantum
phenomena, the weird behaviour of the
subatomic world. In recent months,
huge strides have been taken towards
the development of a ‘quantum internet’.
Such a network would let you Google
for web pages exponentially faster than
you can on a classical computer, make
new types of games possible, and provide
absolutely secure eavesdropper-proof communication so you would never need
worry about casting your bank details into
cyberspace again. Add to this cameras that
could take pictures of things they can’t
see themselves and new techniques for
developing drugs, and it seems
quantum technology is coming of age.
It is perhaps a reflection of this that
two physicists, Professor Serge Haroche
at Collège de France and École Normale
Supérieure, both in Paris, and Dr David
Wineland at the National Institute of
Standards and Technology in Colorado
have both been awarded the 2012
Nobel Prize in Physics for their work
on quantum technology.
Subatomic particles lose their quantum
properties as soon as they interact with
the outside world – something that’s made quantum phenomena difficult to study.
But working separately, Haroche and
Wineland managed to measure and control
particles when they were exhibiting
quantum behaviour for the first time.
With their electric fields and mirrors, they
paved the way for others to experiment
with tiny quantum particles and, most
importantly, put them to use.

QUANTUM DREAMS

It was back in the 1970s when David
Deutsch, an Oxford-based mathematician
and physicist, realised that quantum
phenomena could revolutionise
computing. Down in the quantum world,
physics is very different to our everyday
experience. Particles do funny things,
like being in two states at once (called
superposition) and appearing to be somehow
connected. In the latter, one particle will
do the opposite of the other, even when
separated by a large distance, in an effect
known as ‘entanglement.

SUPERPOSITION



One of the strangest properties of subatomic particles is that they
can exist in two or more states at the same time. An electron,
for example, can be in one of two states determined by its spin.
Quantum spin is very loosely analogous to spin in the everyday
sense except that in the quantum world it’s ‘quantised’, being
allowed to take just one of two values, denoted ‘spin up’ and ‘spin
down’. Each of these configurations is a ‘state’ of the electron.
But an electron can exist in a mix of these two states. And that’s
how they’re used to record a qubit of information, with ‘spin up’
representing ‘1’ and ‘spin down’ as ‘0’.

ENTANGLEMENT

Einstein called it ‘spooky action at a distance’. Subatomic particles
can become linked and remain linked no matter how far they are
separated – one particle doing the opposite of the other. Two
entangled particles taken to opposite sides of the Universe would
exhibit a kind of faster-than-light communication between each
other: measuring the state of one would instantly determine the
state of the other. This entanglement will allow information to
be communicated over vast distances. However, the entangled
channel has to be supplemented by a classical signal which can
never exceed the speed of light. 

DECOHERENCE 



Older physics text books will tell you that a quantum particle
exists as a wave only until someone measures it, at which point
the waviness is destroyed and it becomes a ‘classical’ object. Some
physicists disapproved of the subjective picture this conjured
up. We’ve since discovered that any interaction with the outside
environment is enough to make a particle in a quantum state turn
classical. Physicists refer to this process as ‘decoherence’, and it’s
a major headache in the development of quantum communication
systems in which the quantum state of photons must be preserved
as they travel along miles of fibre-optic cable.

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