2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/19039We study the quantum charge noise and measurement properties of the double Cooper pair resonance point in a superconducting single-electron transistor (SSET) coupled to a Josephson charge qubit. Using a density matrix approach for the coupled system, we obtain a full description of the measurement back-action; for weak coupling, this is used to extract the quantum charge noise. Unlike the case of a non-superconducting SET, the back-action here can induce population inversion in the qubit. We find that the Cooper pair resonance process allows for a much better measurement than a similar non-superconducting SET, and can approach the quantum limit of efficiency.5 pages, 3 figures; factor of two error in last paragraph correctedMesoscale and Nanoscale PhysicsSuperconductivitytext