Throughout history, thinking about the energy of electromagnetic radiation as a continuus value made disagreements with experimental results, so Planck came to the conclusion that the energy was quantized. Quantization actually means that we’re talking about a discrete set of values and in case of energy we can have values that are multiple integers of \( ħω\). The main goal of this thesis is to come to the conclusion that the electromagnetic field is quantized, by analogy with the terms of quantum-mechanical harmonic oscillator. By further analyzing the problem, we will go through some concepts such as the number of photons and vacuum energy, but also the subject of interaction between the field and the atom. In the end, theoretical prediction is compared to the experimental results where damping in probability is observed. One very important conclusion to this thesis is that understanding of the quantization of electromagnetic field solved many historical problems such as ultraviolet catastrophe and photoelectric effect but also some more modern ones such as Casimir effect. Moreover, the consequences are applicable to the development of technology, while quantum computers are just a small step towards a more broad future usage.