  Green-Horne-Zeilinger states are a typical type of multipartite entangled
states, which plays a central role in quantum information processing. For the
generation of multipartite entangled states, the single-step method is more
preferable as the needed time will not increase with the increasing of the
qubit number. However, this scenario has a strict requirement that all the
two-qubit interaction strengths should be the same, or the generated state will
be of low quality. Here, we propose a scheme for generating multipartite
entangled states of superconducting qubits, from a coupled circuit cavities
scenario, where we rigorously achieve the requirement via adding an extra
z-direction ac classical field for each qubit, leading the individual
qubit-cavity coupling strength to be tunable in a wide range, and thus can be
tuned to the same value. Meanwhile, in order to obtain our wanted multi-qubits
interaction, x-direction ac classical field for each qubit is also introduced.
By selecting the appropriate parameters, we numerically shown that
high-fidelity multi-qubit GHZ states can be generated. In addition, we also
show that the coupled cavities scenario is better than a single cavity case.
Therefore, our proposal represents a promising alternative for multipartite
entangled states generation.

Quantum Physics