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

qubits.

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.

2.1.2 Entanglement

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

qubit.

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

intact.

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.