[QUE/QFT-10001]

\(\newcommand{\ket}[1]{|#1\rangle} \newcommand{\matrixelement}[3]{\langle#1|#2|#3\rangle}\)

For a real free Klein Gordon field, mass \(m\),  compute \[ \matrixelement{0}{\phi(x)\phi(y)}{\vec{k}, \vec{q}}\] and show that the result is  properly symmetrized wave function for two identical bosons with momenta \(\vec{q},\vec{p}\). Here \(\ket{\vec{k}, \vec{q}}\) is the state with two bosons with momenta \(\vec{k}, \vec{q}\)