Quantum Computing – Our demand for processing power continues to increase as more people connect to the internet and the integration of computing into our lives increases. Moore’s law is the observation that the number of transistors in a dense integrated circuit doubles approximately every two years postulated by Moore( Co founder of Intel Corp.)
There is a physical limit to how small these components can get, and as they get near the size of an atom, the quirky rules that govern quantum mechanics come into play.
Quantum theory is the branch of physics that deals with the world of atoms and the smaller (subatomic) particles inside them.
Main Difference between Digital Computers & Quantum Computers:
Whereas digital computers require data to be encoded into binary digits (bits), each of which is always in one of two definite states (0 or 1), quantum computation uses quantum bits (qubits), which can be in superpositions of states.
A quantum computer has quantum bits. These are made out of quantum particles that can be zero, one, or some kind of state in between – in other words they can have both values at the same time.
A qubit with superposition is in a much more complex state than the simple 1 or 0 of a binary bit. More parameters are required to describe that state, and this translates to the amount of information a qubit can hold and process.
Applications:

Because a quantum computer can be in all the states at the same time, you just do one calculation so you perform impossible tasks easily.

Size of computers can be drastically reduced and speed can be increased.

Compute – research and algorithms easily then digital computers.

Quantum computers will provide a useful new way of simulating and testing the workings of quantum theory, with implications for chemistry, biochemistry, nanotechnology and drug design.