Measuring the Decoherence of a Quantronium Qubit with the Cavity Bifurcation Amplifier

Understand

Dispersive readouts for superconducting qubits have the advantage of speed and minimal invasiveness.

• We have developed such an amplifier, the Cavity Bifurcation Amplifier (CBA) [10], and applied it to the readout of the quantronium qubit [2].
• It consists of a Josephson junction embedded in a microwave on-chip resonator.
• In contrast with the Josephson bifurcation amplifier [17], which has an on-chip capacitor shunting a junction, the resonator is based on a simple coplanar waveguide imposing a pre-determined frequency and whose other RF characteristics like the quality factor are easily controlled and optimized.