Reading out charge qubits with a Radio-Frequency Single-Electron-Transistor

We describe fabrication and measurements of Single Electron Transistors operated in the Radio Frequency mode (RF-SET). We demonstrate very high sensitivity for RF-SETs and we evaluate the back-action from an RF-SET when used as a read-out device for charge qubits. We conclude that single-shot read-out is possible with a signal to noise ratio greater than one, and that niobium qubits would substantially improve the signal to noise ratio. Furthermore we describe how the RF-SET could be used to read out a differential qubit in a gradiometer coupling.