Readout methods and devices for Josephson-junction-based solid-state qubits

We discuss the current situation concerning measurement and readout of Josephson-junction based qubits. In particular, we focus attention on dispersive low-dissipation techniques involving reflection of radiation from an oscillator circuit coupled to a qubit, allowing single-shot determination of the state of the qubit. In particular, we develop a formalism describing a charge qubit read out by measuring its effective (quantum) capacitance. To exemplify, we also give explicit formulas for the readout time.