# 2

# Quantum Computing Basics

This chapter is devoted to the basic information, techniques and skills required to travel around the quantum world safely. First we introduce quantum phenomena using the strange sounding probabilistic gate in Section 2.1. Quantum computing is rooted in quantum mechanics therefore Section 2.2 explains the postulates of quantum mechanics which form the solid base of any further discussion. Next we build bridges between classical and quantum computing in Section 2.3 and 2.4 where generalization of registers and logic gates are investigated. The following Section 2.5 analyzes an interesting quantum circuit called quantum interferometer. Quantum mechanics offers certain possibilities which are not present in classical computing. The most important one which connects pieces of quantum information very tightly is referred to as entanglement and is introduced in Section 2.6. As in everyday life everything has its price. The price of entanglement has some restrictions e.g. we can use the COPY command in quantum computing as explained in Section 2.7. Finally we show how to prepare an arbitrary quantum state in a quantum register in Section 2.8.

## 2.1 MYSTERY OF PROBABILISTIC GATE

We propose to start getting acquainted with quantum computing and communications by ...