# Linear superposition of single-particle states

1. ### Neitrino

134
Dear all,

I am not sure whether I understand correctly or not.
So from Peskin Schroeder’s book:
$$\phi(x)|0>= \int{\frac{d^3 p}{(2\pi)^3}\frac{1}{2E_p}e^{-ipx}|p>$$
formula (2.41). Interpreting this formula they say – it’s a linear superposition of single-particle states that have well defined momentum. And also that operator phi(x) acting on the vacuum, creates a particle at position x.
My question – since it is a superposition of single-particle states and creates a particle at position X, So that operator creates many single-particle states with different momentum (since there is integration over p and each single-particle state has different momentum) and all of them (particles with different momentum ) are created at one position X?
Or briefly – many different momentum particles are created at one position X?

Thanks

Last edited: Sep 2, 2005
2. ### vanesch

6,189
Staff Emeritus
What's the superposition of a one-particle and a one-particle state ? A two-particle state or another one-particle state ? Answer: another one-particle state. Superpositions of N-particle states are again N-particle states.
So you should view this as ONE particle is created, in a superposition of momentum states, exactly as in NR quantum mechanics, where ONE position state is written as (about the same) superposition of several momentum states.

cheers,
Patrick.