**Introduction**

A quantum computers is based on the phenomenon and laws such as superposition and entanglement of quantum mechanics which is used to increase the processing power of today’s computer. The study of quantum computing is known as **quantum information science**.

**History of Quantum Computing**

The idea of quantum computing which is known as mechanical model of Turing Machine is stuck by Richard Faynman and Yuri Manin in 1981, at MIT. They described that the quantum computers had the potential to simulates the things that classical computer couldn’t do.

In 1994, Peter Shor developed his algorithm allowing quantum computers that had the potential to factorize large number integer much faster than our today’s traditional system and Shor algorithm had the capacity to decrypt RSA- encrypt algorithm. The possibility to break the cryptosystem in hours that take million of years with the help of quantum computers.

In 1996, Lov Grover developed quantum database search algorithm to solve brute force algorithm 4 times faster. In 1998, the new era of computing power began where a 2- qubit quantum computer was build to solve Grover’s algorrithm.

In recent years, the research of quantum computing has increased both in public and private sectors. In 2017, IBM presented the first commercial useable quantum computer, that raising the level of interest in this field. On 23 October 2019, Google AI, in partnership with the U.S. National Aeronautics and Space Administration (NASA), published a paper in which they claimed to have achieved quantum supremacy.

**What is Qubits?**

A classic computer represent any information in the form of 2 bits either 0 or 1. But a quantum computers uses either 0 or 1 and superposition of 0 or 1, in other words 0 or 1 both at same time. So the classic computer can perform one calculation at a time but quantum computers can perform many operation and calculations at a same time. With the help of qubits the complex algorithm that can solved by classical computer in million of years, a quantum computers can solve those algorithm with in few hours or days.

** **

** **

**Superposition**

One of the properties that sets a qubit apart from a classical bit is that it can be in superposition. Superposition is one of the fundamental principles of quantum mechanics. In classical physics, a wave describing a musical tone can be seen as several waves with different frequencies that are added together, superposed. Similarly, a quantum state in superposition can be seen as a linear combination of other distinct quantum states. This quantum state in superposition forms a new valid quantum state. Qubits can represent numerous possible combinations of *1 *and *0 *at the same time. This ability to simultaneously be in multiple states is called superposition.

**Entanglement**

One of the other counter-intuitive phenomena in quantum physics is entanglement. A pair or group of particles is entangled when the quantum state of each particle cannot be described independently of the quantum state of the other particle(s). The quantum state of the system as a whole can be described; it is in a definite state, although the parts of the system are not. Adding extra qubits to a quantum machine produces an exponential increase in its number-crunching ability is called entanglement

**Applications of Quantum Computers**

**Artificial Intelligence and Machine Learning:-**Today the era of artificial intelligence and machine learning more and more complex algorithm takes lots of computing power and processing time to solve by classical computers which can be easily solved and take less time by quantum computing.

** **

**Financial services:-**To solve this, investors and analysts have turned to quantum computing. One immediate advantage is that the randomness inherent to quantum computers is congruent to the stochastic nature of financial markets.

** **

**Cryptography:- :-**Today online security currently depends on the difficulty of factoring large numbers . Quantum computers can perform such factoring exponentially more efficiently than classical computers, which help security much stronger than earlier.

**Weather Forecasting:- **“Using a classical computer to perform such analysis might take longer than it takes the actual weather to evolve!” This motivated Lloyd and colleagues at MIT to show that the equations governing the weather possess a hidden wave nature which are amenable to solution by a quantum computer.