# Single electron wave packet in Fock space?

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1. Jun 22, 2015

### MisterX

How might we construct a state most closely corresponding to the idea of a single electron wave packet as some superposition of Fock states?

2. Jun 23, 2015

### Staff: Mentor

I don't think that's compatible with the QFT formalism of a superposition of 0 particle, 1 particle, 2 particle states etc - but someone who knows more than I do may have an answer - I certainly don't. A wave-packet is of a single particle.

Thanks
Bill

3. Jun 23, 2015

### A. Neumaier

It is a pure Fock state in its 1-particle sector. A general Fock state has the form $$\psi=\psi_0+\psi_1+\psi_2+\ldots$$ of a superposition of N-particle states \psi_N. In a momentum representation the latter are of the form $$\psi_N=\int dp_1...dp_N \psi_N(p_1,\ldots,p_N)|p_1,\ldots,p_n\rangle$$. Now put all \psi_N to zero except for N=1, and you can translate your wave packet exactly into a state in Fock space.

Last edited: Jun 23, 2015