*by*

**Reetobrata Chatterjee**

A quantum computer is a computer
which makes use of the quantum states of sub-atomic particles in order to store
and manipulate information. Put simply, this allows us to have a computer which
works MUCH faster than normal computers. If a semi-decent quantum computer
could be constructed (current efforts have very small amounts of computing
power), then the entire banking industry and others could collapse before our
very eyes.

A standard computer works very simply.
All the data you provide is stored as a combination of 1s and 0s, using ever
tinier devices called transistors, which have an on (1) or off (0) state. The
data in each transistor is known as a bit, and they work in groups of 8, as
bytes. As these bytes build up, you get kilobytes, megabytes and so on. This
allows a group of n transistors to be in one of 2

^{n}states. More powerful computers have more transistors or those of a higher quality which fail less often.
But not quantum computers.

They use an entirely different way
to store the data. This is called a qubit. Unlike a transistor, which can
either be 1 or 0, using the ideas of quantum superposition to be 1 or 0 or both
at once. This is similar to Schrodinger's cat, which was both dead and alive until the box was opened (If
you don’t know what SchrÃ¶dinger’s cat is, the video explains it really well).

This is achieved by using coils of
a special metal called Niobium. If the current goes through the loop
counter-clockwise, it will create a tiny magnetic field pointing up, whereas a
clockwise current will have a downwards facing magnetic field. These are the
equivalent of the classical 1 and 0 states. Drop this however to 0.2° C above
absolute zero and the coils begin behaving like superconductors, wires with
basically 0 resistance. This allows the system to enter the mysterious expanses
of quantum superposition, where each individual qubit, could be 1 or 0, or
since it’s superposed, both.

#
How will this affect us?

The government, banks and Facebook
(and all other websites) all use encryption to keep your data safe and away
from people who might want it for malicious purposes. The tightest security
around this data, is while it’s being transmitted and stored. Generally this is
in the form of public key encryption.

Take the number 10. If someone
asked you to find its factors, it would be very simple (5 and 2). Now take the
number 4453. Finding the factors of this are just a little bit harder. But a
computer could do it. (The factors are 61 and 73 by the way, what makes this so
difficult is that they have only 2 prime factors). If you now replace this
number by one which is hundreds of thousands of digits long, which have only 2
prime factors, each thousands of digits long, the task becomes rather
difficult. The current estimation to crack a 1024 bit RSA key, which is
essentially a really, really large number with only 2 factors is 5.95 x 10

As a comparison the universe is 13.75 x 10

^{211}years.As a comparison the universe is 13.75 x 10

^{9}years old.
But this calculation is only
limited to traditional computers.

A powerful quantum computer, on the
other hand, could do this calculation in a few hours purely passed on the fact
that for every bit you add to it, it becomes exponentially as powerful.

Fear not however, your money,
messages and snapchats are safe (for now) because the largest number factorised
on a quantum computer is 56153, not small, but insignificant compared to the largeness
of the numbers in current encryption techniques.

Michael Crichton's novel 'Timeline' deals with quantum computers quite well and accurately, well worth a read (as well as quantum teleportation and medieval France)

ReplyDeleteTim Bustin