We propose a scheme to achieve a kind of nontrivial multipartite pair-wise controlled phase operation in a cavity QED setup. The operation implemented is of geometrical nature and is not sensitive to the thermal state of the cavity. In particular, we have managed to avoid the conventional dispersive coupling so that high speed gate operation is achieved which is very important in view of decoherence. We show that this multipartite pair-wise controlled phase operation makes the generation of two-dimensional cluster states very efficient.
We propose a scheme to achieve a kind of nontrivial two-qubit operation using controllable electrons in double-dot molecules coupled to a transmission line resonator.The implemented operation is geometrical in nature and insensitive to the state of the transmission line resonator.In particular,we are able to avoid conventional dispersive coupling so that a high speed gate operation can be achieved,which is important in view of decoherence.Meanwhile,we are able to further generalize the operation to an arbitrary phase case by dynamic decoupling with two sequences.
Based on the rapid experimental developments of circuit QED,we propose a feasible scheme to simulate the spin-boson model with superconducting circuits,which can be used to detect quantum Kosterlitz-Thouless(KT) phase transition.We design the spinboson model by using a superconducting phase qubit coupled to a semi-infinite transmission line,which is regarded as a bosonic reservoir with a continuum spectrum.By tuning the bias current or the coupling capacitance,the quantum KT transition can be directly detected through tomography measurement on the states of the phase qubit.We also estimate the experimental parameters using the numerical renormalization group method.
