Dispersive microwave readout for quantum electrical circuits

Over the past decade, quantum coherent behavior has been observed in electrical circuits engineered to have discrete, individually addressable energy levels. These devices operate at cryogenic temperatures and microwave frequencies—conditions which permit the utilization of superconducting passive and active resonant circuits for measurement. The basic architecture of a quantum dispersive measurement consisting of a two level quantum bit coupled to a LC tank circuit is reviewed. Recent progress with this type of readout has led to the real time monitoring of a superconducting qubit with the observation of quantum jumps between energy levels.