The theoretical studies of computation systems which makes the direct use of quantum – mechanical phenomena, such as superposition and entanglement to perform operations on data is called quantum computing. Quantum computers are different from binary digital electronic computers. Binary digital electronic computer uses binary digit 0 and 1 where as quantum computation uses quantum bits which can also be superposition of both 0 and 1. The field of quantum computing was initiated by the work of Paul Benioff and Yuri Manin in 1980. By the change of time many others took a initiative to develop it.

### What is a qubit?

A qubit just like a classical bit has two possible states | 0 > and (denoted in dirac notation ). But unlike classical bit a qubit can be in more than two possible states. That is, it can be in a superposition of states and . Mathematically, a superposition state looks like,
In the above expression is the probability amplitude for state and β is the probability amplitude for state . and both can be complex numbers. Since and are probabilities amplitudes, they must be normalized. Mathematically,

Qubits can be represented in terms of polarization of a photon where vertical and horizontal polarization are the two states. It can also be represented in terms of spin of an electron. There are number of quantum computing models distinguished by the basic elements in which the computation is decomposed.

### Quantum Computing Models

**Adiabatic quantum computer based on quantum annealing**

Here, the computation gets decomposed into a slow continuous transformation of an initial Hamiltonian (is a operator corresponding to the total energy of the system in quantum mechanics) into a final Hamiltonian whose ground state contain the solution.

**One way quantum computer**

The computation decomposed into sequence of one quantum bit measurements applied to a highly entangled initial state or cluster state.

**Topological quantum computers**

The computation decomposed into the brading of anyons in a 2D lattice.

Quantum gate array: The computation decomposed into sequence of few quantum bit quantum gates.

A quantum bit can hold even more information, e.g. up to two bits using superdense coding. Hence, quantum computers will be able to analyze the vast amount of data collected by telescope and seek out earth like planet. The concept of quantum computational models will help to determine how diseases developed. Google itself is using a quantum computer to design software that can distinguish cars from landmarks.

A quantum may be the smallest measurable finite unit but quantum computing may unlock doors to infinity. It is expected to be the next biggest invention in computing despite the fact that most experts concede that the first quantum computer may be some years off.

Research Blog: What is a Quantum Bit?