Quantum dynamics of superconducting nano-circuits: phase qubit, charge qubit and rhombi chains

We have studied different quantum dynamics of superconducting nano-circuits with Josephson junctions. A dc SQUID, when it is strongly decoupled from the environment, demonstrates two-level and multilevel dynamics. We have realized a two qubits coupled circuit based on a dc SQUID in parallel with an asymmetric Cooper pair transistor (ACPT). The ACPT behaves as a charge qubit. Its asymmetry produces a strong tunable coupling with the dc SQUID which is used to realize entangled states between the two qubits and new read-out of the charge qubit based on adiabatic quantum transfer. We have measured the current–phase relations of different rhombi chains in the presence or absence of quantum fluctuations which confirm theoretical predictions.