Qubit dispersive readout scheme with a microstrip squid amplifier

A flux qubit readout scheme involving a dispersive technique coupled to a microstrip squid amplifier has been tested experimentally. Thanks to the almost quantum limited noise of this amplifier at low temperature, this readout device is very promising for a design with actual qubits. It's proof of principle and low noise performance have been tested by simulating the qubit presence applying a tiny flux change in the input squid. The resonant frequency of the amplifier is adjusted in-situ with a varactor diode to approach the frequency of the tank circuit. Depending on the sign of the transfer function, two operating mode (crossing or anticrossing regime) have been identified.