# Problems on quantum field operators in QFT

by Dyson
Tags: field, operators, quantum
 P: 21 Hello! I met some annoying problems on quantum field operators in QFT.They are as follows: (1)The quantum field operator( scalar field operator, for example),is often noted as φ（r,t). Can it be interpreted as like this: φ（r,t) is the coordinate represetation of a more abstract,theoretical operator φ in Hilbert space? (2)Is there exist the represetation(such as momentum, coordinate.....) which is similar to that in quantum mechanics in QFT? Thanks for reply!!!
 Sci Advisor P: 5,295 Regarding 1) no, r is an "index", not an entity living in a Hilbert space. This becomes clear if one derives quantum field theory of a scalar field from infinitly many coupled harmonic oscillators. Regarding 2) yes, these are the so-called creation an annihilation operators obtained by Fourier transform of the field operators, usually denoted as $$a^\dagger(p)$$ and $$a(p)$$
P: 21
 Quote by tom.stoer Regarding 1) no, r is an "index", not an entity living in a Hilbert space. This becomes clear if one derives quantum field theory of a scalar field from infinitly many coupled harmonic oscillators. Regarding 2) yes, these are the so-called creation an annihilation operators obtained by Fourier transform of the field operators, usually denoted as $$a^\dagger(p)$$ and $$a(p)$$
Thank you very much!

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