be counterintuitive, it is what will empower
quantum computers to be significantly faster
that classical computers.Superposition allows
quantum computers to process more information
and process multiple scenarios at once.
Classical bits, shown by the diagram on the
left can be in either state 1 or state 0.
Qubits, as shown by the diagrams on the left
can be in superposition in multiple states
at once.
For example in the diagram, the one qubit
is in a superposition of one, zero and some
complex states in between.
The diagram on the right shows five qubits
in superposition.
These five qubits can be in 32 different states
at once, in contrast to five classical bits,
which can only be in 5 states.
This means that the qubits can process large
amounts of information in parallel, which
make them efficient in some types of problems.
So what are these qubits in a quantum computer?
In a quantum computer, the qubits can be many
things, but the most common forms of qubits
are the spin of an electron or the polarization
of a photon or the nuclear spin of an atom,
with some value of each quantum property representing
a state.
Now you know what qubits are, and what makes
them special, but how do quantum computers
use these qubits to actually process information?
At first, all n qubits in the quantum computer
are 
put into a superposition of 2n states.
The problem that the computer is trying to
solve is then encoded into this superposition.
So our qubits are put into a superposition
of all possible solutions to our problems.
Then by performing operations on our particles,
we can transform and/or analyze all of the
solutions encoded in our superposition at
once.
This is what grants quantum computers significant
advantages over classical computers when solving
specific types of problems.
However, there is catch.
When the quantum particles are measured after
the algorithm is completed, the superposition
is collapsed and one of the many possible
solutions in the superposition is measured
at random, and all others are lost.
We would seem to be no better off than if
we used a classical computer and tried out
one randomly chosen possible solution—in
either case, we end up knowing about only
one possible solution.
Thankfully, at the quantum scale particles
can be represented as both particles and waves.
This allows quantum algorithms take advantage
of wave interference.
Wave interference refers to how waves in phase
add and waves out of phase cancel each other
out [Show diagram, wave interference].
Waves whose crests and troughs align are in
phase and will add, called constructive interference,
whereas waves whose crests and troughs are
not at the same places will subtract called
destructive interference.
Quantum algorithms exploit this property.
In superposition, when incorrect solutions
are detected, destructive interference is
used to cancel out these incorrect solutions
. Whenever potential correct solutions are
detected, then constructive interference is
used to increase the probability that these
correct solutions are measured at the end.
This leads to extremely high probabilities
of measuring the correct solution at the end
of the computation.
So, after the qubits are placed in superposition,
the problem is encoded onto these qubits,
and operations are performed on all qubits
at the same time, and wave interference is
used to eliminate incorrect solutions, ultimately
providing the correct solution at the end
of the computation.
Quantum computers operate on completely different
principles to existing computers, which makes
them really well suited to solving particular
mathematical problems, like factoring very
large prime numbers.
This provides quantum computers with many
benefits over classical computers allowing
to solve many types of problems that classical
computers could potentially take years to
solve.
An example of this is simulations of complex
chemicals.
In order to fully simulate a chemical reaction,
a large amount (billions or trillions) of
sub-atomic particles have to be simulated.
Electrons in a chemical exert a charge on
every other electron in the chemical.
This means that every time something is changed
the charge, position and many other properties
of each and every sub-atomic particle have
to be re-calculated.
This makes it an extremely difficult task
for classical computers.
However, quantum computers can simulate these
reactions much more effectively and efficiently
than classical computers, taking advantage
of their superposed and entangled qubits.
The simulation of chemicals and other sub-atomic
particles can lead to making of better medicines
and an overall better understanding of chemistry
and how sub-atomic particles interact with
each other.
So why don't we have quantum computers yet?
So far, the largest and most powerful quantum
computers have less than 50 qubits.
In contrast, a classical computer with 8 Gb
of ram has 64 million bits.
One of the factors constraining the growth
of quantum computers is their physical size.
Even though most quantum computers today only
have a small number of qubits, they still
occupy an extremely large amount of space.
These quantum computers need to be made smaller
before they can be made bigger.
Another problem is that the sub-atomic particles,
like electrons and photons that are used in
quantum computers begin to become unreadable
and loose their superposition as they interact
with their environment.
This process is called quantum decoherence.
In order to prevent this, complete isolation
of the qubits is required.
However, this is not feasible, but this is
also the reason why qubits are kept at extremely
low temperatures, to prevent decoherence.
The final goal is to create a quantum computer
with over 100,00 qubits.
So, in summary, a quantum computer uses special
quantum bits to store and process information.
These quantum bits can be in multiple states
at once, allowing for operations to be run
on large amounts of data and numbers all at
the same time.
Quantum computing would be beneficial for
cryptography and encryption, by providing
methods of encrypting data that would be almost
impossible to breach, it would be beneficial
for medicine and chemistry by allowing complex
chemical reactions to be simulated accurately,
leading to the creation of better medicine.
Quantum computers would also have benefits
for searching large amounts of data, machine
learning and AI as well as any kind of optimization
problems, but there are still some challenges
to overcome before this can be actually created.
