In early 19th century, Charles Babbage started a
new era of computers by inventing the first mechanical computer. Then, Richard
Feynman, a physicist, intrigued a bizarre revolution in the era by urging the
world to build a quantum computer.
The basis of invention of quantum computer lies in a thought
experiment, the Schrodinger’s Cat, in which a cat is theoretically both alive
and dead at the same time. This is the unpredictable nature of quantum
mechanics. Similar to this, the researchers and scientists made some ions to
exist in two states simultaneously by creating an effect called entanglement. This,
in itself, is challenging the very fabric of reality.
2.1 How can a Quantum
Computer be made?
2.1.1 0s, 1s and both
In our macroscopic world, everything is expected to be clear
and distinct but at microscopic level, this is neither necessarily required nor
is this possible. For example, electrons and photons, these tiny particles
exhibit different states simultaneously. This fact provided the basis of
Unlike the classical computers that work on binary bits, 0s
and 1s, the quantum computers work with particles which represent qubits. The sequence
of qubits consists of the 1 and 0 state along with the quantum superposition of
these two states, providing different energy levels to the qubits. Such qubits
are known as qudits.
Qubits create non-trivial correlated states of different number
of qubits. These states are known as entangled states. And describing a system
of several qubits with all the correlations between them using the ordinary
classical information is known as entanglement. As the number of qubits in a
system increase, increases the number of their correlations, that too,
exponentially, which provides us a relation that if there are n number of qubits in a system, then the
number of correlations between them is 2n.
2.1.3 Topological Qubits
Scientists haven’t yet found a simple way to control the
complex systems of qubits. So building a computer with today’s qubits is like a
tall, narrow tower with the blocks; the more you add the less stable it
becomes. Seeing these limitations Microsoft Inc. announced another solution to
achieve the goal by building a more stable qubit, which it called topological
Qubits store the
information in volatile states which are easily prone to be lost, like a sand
painting, whereas the topological qubits store the information in a more stable
form, like a knot in a thread, whatever happens to the thread, the knot remains
It is believed that once a topological qubit is built, building
a stable quantum computer on a large scale would become possible.
2.2 Quantum Computers v/s Classical Computers
Qubits exhibit the unique behavior of the tiniest objects in
the world. Quantum Mechanics allows qubits to store much more complex
information than traditional bits so that each qubit added to the computer
doubles its processing power, an exponential gain which is not possible with
the classical computers.
Considering an example of entanglement, if there exists a
system of 200 qubits, to describe its 2200 correlations, numbers
fall short, i.e., classical bits cannot help to write the information contained
in a few hundred qubits system. This gives a reason to think that a quantum
computer can perform tasks that a classical computer can’t.