GRW localization operator ($L_i(\mathbf{X})$)

For localization length $r_C$, the GRW localization operator acting on particle $i$ isA collapse centred at $\mathbf{X}$ sends $|\psi ⟩$ to the normalized state $L_i(\mathbf{X})|\psi ⟩$ with probability density $\Vert L_i(\mathbf{X})|\psi ⟩{\Vert }^2$.