When the law of physics gets failed for the smallest units. Then the law of quantum physics starts to take over. The sub atomic particles behave like waves instead of particles itself. They can instantaneously send information over a vast distance. But it is fascinating that it appears to be on 2 different places at the same time.
Now, our computer has information in bits (it can be either one or zero) but in quantum computing the bits can be both 1 and 0 at the same time and we call it Qubit. So it has not to do all the steps of computing though it can execute all the steps of computing at the same time. So it will be exponentially faster than the fastest computer ever existed.

Writing about history, it all started when Richard Feynman and Yuri Manin expressed the idea that a quantum computer had the potential to simulate things that a classical computer could not. In 1994, Peter Shor published an algorithm that is able to efficiently solve some problems that are used in asymmetric cryptography that are considered hard for classical computers.

I had seen a video where it has been shown that IBM is in the process of creating a quantum computer and the sound of it was the sound of the future. However, it needs almost extreme cold temperature to manage such computers. Most of the readers must have watched "ant-man and the wasp" where they travel in the quantum realm. Who knows when one day will come and we can also get smaller in size to visit the quantum realm.