Where does the 1/√N factor in the Dicke model arise from?

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SUMMARY

The 1/√N factor in the Dicke model arises from the Holstein-Primakoff transformation, which expresses spin operators in terms of harmonic oscillator operators. This transformation introduces a √N factor that cancels with the definition of the coupling constant, ensuring the correct asymptotic behavior in the high N limit. The Hamiltonian for N two-level atoms interacting with a single mode of an electromagnetic field is accurately represented by the equation: \hat{H}_{D}=\omega_{A}\hat{J}_{z}+\omega_{F}\hat{a}^{\dagger}\hat{a}-\frac{\gamma}{\sqrt{N}}\left(\hat{J}_{-}\hat{a}^{\dagger}+\hat{J}_{+}\hat{a}\right)-\frac{\gamma}{\sqrt{N}}\left(\hat{J}_{+}\hat{a}^{\dagger}+\hat{J}_{-}\hat{a}\right).

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lfqm
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Hello colleagues, hope you can help me.

The Dicke model describes a system of N two-level atoms cooperatively interacting with a single mode of an electromagnetic field as follows:

\hat{H}_{D}=\omega_{A}\hat{J}_{z}+\omega_{F}\hat{a}^{\dagger}\hat{a}-\frac{\gamma}{\sqrt{N}}\left(\hat{J}_{-}\hat{a}^{\dagger}+\hat{J}_{+}\hat{a}\right)-\frac{\gamma}{\sqrt{N}}\left(\hat{J}_{+}\hat{a}^{\dagger}+\hat{J}_{-}\hat{a}\right)

In the case of a single atom the factor turns into 1, and the hamiltonian of the N atoms should be the sum of N single atom hamiltonians, right? So, where does the 1/√N factor arise from?

Thanks!
 
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Actually, it was the first link in google searching for "Dicke model" not related to fat female models ("dicke" means fat, in German) :-)
 
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