Abstract: During this thesis, we have used superconducting circuits with Josephson junctions, derived from the Cooper pair box, in order to implement quantum bits (qubits). To implement two‐qubit gates, we have developed a new circuit, the quantroswap, which consists in two capacitively coupled Cooper pair box, each of them being manipulated and read separately. We have demonstrated coherent exchange of energy between them, but we have also observed a problem of qubit instability.
In order to avoid this spurious effect, we have implemented another circuit based on a charge insensitive split Cooper
pair box coupled to a non‐linear resonator for readout‐out purpose. We have measured large coherence time, and obtained large readout fidelity (90%) using the bifurcation phenomenon. For metrological purpose, microwave reflectometry measurement on a quantronium also allowed us to relate an applied current I to the frequency f=I/2e of induced Bloch oscillations.
IRAMIS-SPEC/Groupe Quantronique