What is wick theorem?

The Wick theorem is a mathematical formula used in quantum field theory to simplify calculations of quantum processes. Specifically, it expresses an expectation value of a product of operators in terms of a sum of all possible pairs of contractions between the operators.

In other words, the Wick theorem allows for the simplification of complex equations involving quantum field operators by reducing them to a series of contractions between pairs of operators. This makes computations much easier and faster, allowing physicists to make more progress in their research.

The theorem is named after Gian-Carlo Wick, who developed it in the 1950s. It has since become an essential tool in many areas of theoretical physics, including quantum electrodynamics, quantum chromodynamics, and quantum field theory in general.