In 1982, Richard Feynman, a Nobel prize-winning physicist thought up the idea of a 'quantum computer', that uses the effects of quantum physics and quantum mechanics to its advantage. The notation of a quantum computer was primarily of a theoretical interest only, but recent years developments have gain attention of the world’s popular researchers. For example, the development was the invention of an algorithm to factor large numbers on a quantum computer, by Peter Shor (Bell Laboratories). By using Shor’s algorithm, the quantum computer would be able to crack codes much more quickly than any ordinary (or classical) computer could perform. By the way a quantum computer is capable of performing Shor's algorithm that would able to break current cryptography techniques in a fraction of seconds. With the motivation provided by Shor’s algorithm, quantum computing has gathered momentum and great interest in researchers around the world are racing to be the first to create a practical quantum computer.

The
word quantum derived from the
Latin word quantus which means
“how much”. Quantum is a discrete quantity of energy proportional in magnitude
to the frequency of the radiation. An analogue discrete amount of other
physical quantity, such as momentum or electric charge is known as quantum.

The
only comprehensible unit by the computer is a bit (binary digit either 0 or 1) which is the smallest. So bit
is the basic unit of the classical computer. One of the most intuitive
representation of bit is an open(on) or closed(off) switch of the circuit. In
today’s modern computer, this representation remains in transistors, with a
high voltage possibly denoting a 1 and low voltage possibly denoting a 0. A two
state system (0 to 1) is the building block of classical computational device.

A
quantum computer is nothing like a classical computer in design; you can't for
instance build one from diodes and transistors. In order to design, a new type
of technology is required, a technology that enables ‘quantum bits' to exist as
coherent superposition of 0 and 1 state. A quantum bit or simply qu-bit
is a unit of quantum information. Qu-bit represents both the state
memory and the state of entanglement in a system. Quantum entanglement is experimentally verified property of
nature. It happens when the particles such as photon, electron, molecules
interacts physically and then become separated. This is known as entanglement.

An
example of an implementation of the qu-bit is the quantum dot which is the first step taken by the researchers for
building a quantum computer. In this phenomenon a single electron is trapped
inside a cage of atoms. When the dot (i.e. the electron) is exposed to a pulse
of laser light of certain frequency λ for the time interval T, the electron is
raised to an excited state: a second burst of laser light causes the electron
to fall back to their ground state. The electron ground state and excited state
can be thought of as the 0 and 1 states of the qu-bit and the application of
the laser light can be regarded as a controlled NOT method as it knocks the qu-bit
from 0 to 1 or from 1 to 0. It would therefore seem that quantum dots are a
suitable candidate for designing a quantum computer. By the way, there are
number of practical problems that are preventing this from happening:

1. The
electron only remains in its excited state for about a microsecond before it
falls to the ground state.

2. There
is a limit to the number of computational steps.

3. Constructing
quantum dots is a very difficult process because they are very small. A quantum
dot measures, 10 atoms (1 nanometer) across.

The
technology needed to build a computer from these dots doesn't yet exist. In the year
2011, Columbia based company D-Wave Systems demonstrated the world’s first
commercially quantum computer D-Wave
one operating on 128 qu-bit processor named Rainie. It performs single mathematical method named discrete
optimization. By using quantum annealing, it also solves optimization problems.
Some researchers found later that this system produce no speedup compared to
classical computers.

It
is sure that quantum computers replace silicon chip, like transistors that
replaced the vacuum tubes. But for now on, the technology requisite to develop
a full-fledged quantum computer is beyond the reach. In most research in
quantum computing are still theoretical.

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