Why is the total capacitance for the CPB-circuit a sum

Question

In this document  (p.6 eqn. 2.1) and also in the general literature for the the basic Cooper pair box circuit the total capacitance $C_\Sigma$ is the sum of the gate-capacitance $C_g$ and the capacitance of the Josephson-Junction $C_J$. Why is that the case? As far as I can see the elements are connected in series and thus only the inverses add up to the inverse of the total capacitance. What am I missing? Are  the capacitances actually connected in parallel? If so can somebody explain why they are considered in parallel, because I don't understand it.

Thanks in advance!

Comments

the junction is not a serial circuit. The 2 capacitors of the pass filters ( meaning 99.99% of the total junction capacitance ) are embeded in // circuits. Very interesting question when linked to a scale description... Perhaps to move to the chat forum?