Measurement of two-qubit states by a two-island single-electron transistor

We solve the master equations of two charged qubits measured by a single-electron transistor (SET) consisting of two islands. We show that in the sequential tunneling regime the SET current can be used for reading out results of quantum calculations and providing evidences of two-qubit entanglement, especially when the interaction between the two qubits is relatively weak compared to qubit-SET coupling.