We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling them to a nanomechanical resonator. We also show that it is possible to implement a two-qubit logic gate between the two charge qubits by choosing carefully the interaction time.
We propose a scheme for generating squeezed states of a nanomechanical resonator. The scheme is based on a hybrid system consisting of two NAMRs and a superconducting charge qubit (SCCQ). The nonlinear interaction between the two nanomechanical resonators (NAMRs) can be implemented by setting the external biased flux of the SCCQ at some certain values, which plays the role of “nonlinear media”. The noise in the SCCQ does not need to be considered, since we can adiabatically keep the SCCQ at the ground state. In addition, the squeezing parameters can also be adjusted by changing the external driving voltage.
We describe a possible implementation of the nanomechanical quantum superposition generation and detection scheme described in the preceding, companion paper (Armour A D and Blencowe M P 2008 New. J. Phys. 10 095004). The implementation is based on the circuit quantum electrodynamics (QED) set-up, with the addition of a mechanical degree of freedom formed out of a suspended, doubly-clamped segment of the superconducting loop of a dc SQUID located directly opposite the centre conductor of a coplanar waveguide (CPW). The relative merits of two SQUID based qubit realizations are addressed, in particular a capacitively coupled charge qubit and inductively coupled flux qubit. It is found that both realizations are equally promising, with comparable qubit–mechanical resonator mode as well as qubit–microwave resonator mode coupling strengths.
We propose some quantum logic gates by using SC-charge qubits coupled to a resonator to study two types of quantum operation. By applying a classical magnetic field with the flux, a simple rotation on the target qubit is generated. Single and two-qubit gates of quantum logic gates are realized. Two-qubit joint operations are firstly generated by applying a classical magnetic field with the flux, and secondly by applying a classical magnetic field with the flux when qubits are placed a quarter of the distance along the resonator. A short discussion of fidelity is given to prove the success of the operations in implementing these gates.