What is the propagation amplitude of a particle in QFT?

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Hola everybody, this is my first visit to PF.
Can anyone help me please...my question is from QFT textbook
phi(x)|0> is creation of particle at position x, being in superposition of momenum states - - - - correct?
<0|phi(y) is birth of particle at position y. So if I consider both expressions i have two particles one born at position x, another particle born at position y.

Phi (x) Phi (y) already in Heisenberg picture.

Why <0|phi(y)phi(x)|0> why is this the propagation amplitude of particle from x to y as said in Peskis and Schroeders book? I have just two particles at x and y, One particle has been created at x, another at position y.

Gracias
 
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