In today’s world we need somewhat advanced way of technology; Quantum Computing uses quantum mechanical phenomena (superposition and entanglement for performing computing. Quantum mechanical tells about physical properties of nature over an atomic scale. The computers performing quantum computations are called Quantum Computers. Quantum Computers solves problem which lies under RSA encryption, faster than classical computers. Quantum Computing is a subfield of Quantum Information. It was begin in 1980s. It was a time when Paul Benioff proposed a quantum mechanical model for turning machine. Later, some scientist suggested that quantum computers have potential to do the task which classical computers can’t do. Out of several models of Quantum Computing, the Quantum Circuit is most widely used model. Quantum Circuits are based on the quantum bits, who somewhat analogous to bit in the classical computation. There are two main approaches to physically implementing a quantum computer: analog and digital. Both approaches use quantum bits. Digital Quantum Computer uses quantum logic gates to do computation. Analog Quantum Computers are further divided into three different approaches: Quantum Simulation, Quantum Annealing and Adiabatic Quantum Computation. In spite of factorization and discrete logarithms, quantum algorithms offering a more than polynomial speedup over the best known classical algorithm have been found for several problems. Quantum Computers provide polynomial speedup for some problems. The famous example for this is Quantum Database Search, which might be solved by Grover’s algorithm using quadratically fewer queries to the database than that are required by classical algorithms. Problems or issues that can be solved with Grover’s algorithm must no searchable structure in the collection of possible answers, the number of possible answers should be same to the number of inputs to the algorithm and there exists a Boolean function which evaluates each input and determines whether it is the correct answer. For problems with all these properties, the running time of Grover’s Algorithm on a quantum computer will scale as the square root of the number of inputs (or elements in the database), as opposed to the linear scaling of classical algorithms. The Quantum Algorithm for linear system of equations or HHL Algorithm is expected to provide speedup over classical counterparts. HHL Algorithm is named after its discoverers Harrow, Hassidim and Liyod. There are many technical issues while building a quantum computer so one should take care about  scalable physically to increase the number of quantum bits, Quantum bits that can be initialized to arbitrary values, Quantum gates that are faster than decoherence time, Universal gate set, Quantum bits that can be read easily for making a good and working quantum computers. One of the major challenges for building quantum computer is about controlling or removing Quantum Decoherence. Time-consuming tasks may render some quantum algorithms inoperable, as maintaining the state of quantum Bits for long enough duration will eventually corrupt the superpositions. The four main Quantum Computing Models are Quantum Gate Array, One-Way Quantum Computer, Adiabatic Quantum Computer, and Topological Quantum Computers. To know more about IT related stuff stay tuned with Oriol Infotech. Visit on www.oriolinfotech.com