# Quantum Gates-Explained

Quantum computing can be hard and intimidating in the beginning. But it will get easier with practice. With this article, I’m hoping to get you started with quantum computing with ease. First, you have to understand qubits.

**Classical bit vs Qubit**

In classical computers, the bit values can either be 0 or 1. In the case of a quantum computer, the “qubits” can take the coherent superposition of both 0 and 1 simultaneously. The qubit is represented with the probabilities of it being a 0 and 1.

This property of qubit is what makes quantum computers exponentially faster than a classical computer. For a given number of bits(n), a quantum computer will perform a calculation 2^n times faster than a classical computer.

Example: With 3 qubits of data, the Quantum computer can store all the 8 possible combinations of 0 and 1 simultaneously. As a result, 4 Qubit based Quantum computer does calculations 16 times faster compare to a 4-bit classical computer.

Now let’s take a look into quantum gates.

**Hadamard Gate**

The Hadamard gate is the most common and the most used quantum gate in quantum computing. It is a single qubit operation that maps the basis state ∣0＞ to ( |0＞ + |1＞)/√2 and ∣1＞ to ( |0＞ — |1＞)/√2, thus creating an equal superposition of the two basic states. This means the measurements will have equal probabilities to become 1 or 0.

**Pauli-X gate**

The Pauli-X gate is a single qubit operation gate that is similar to the classical not gate. It takes a value and flips it to the opposite one. It maps |0＞ to |1＞ and |1＞ to |0＞.

**Pauli-Y gate**

The Pauli-Y gate is a single qubit operation. It maps |0＞ to -i|1＞ and |1＞ to i|0＞. It equates to a rotation around the Y-axis of the Bloch sphere by pi radians.

**Pauli-Z gate**

The Pauli-Z gate is a single qubit operation. It maps |1＞ to -|1＞ and it leaves |0＞ unchanged. It equates to a rotation around the Z-axis of the Bloch sphere by pi radians.

**Controlled gates**

The controlled gate is a 2 or more qubit operation, where 1 or more qubits act as a control for some operation on a qubit. (eg: cx, cy, cz gates)

**Controlled X gate**

The controlled-x gate acts on 2 qubits and performs the NOT operation on the second qubit only when the first qubit is |1＞.

**Conclusion**

I have attached some links to learn quantum mechanics and quantum computing. I hope it helps.

Quantum Computing: https://www.youtube.com/playlist?list=PLOFEBzvs-Vvp2xg9-POLJhQwtVktlYGbY

Quantum Mechanics: http://ocw.mit.edu/8-04S16