Simplify proposal for realizing multiqubit tunable phase gate in circuit QED

Understand

We propose a scheme to realize a multiqubit tunable phase gate in a circuit QED setup where two resonators, each coupling with a qudit, are interconnected to a common qudit (d=4).

• In this proposal, only two levels of each qudit serve as the logical states and the other two levels are used for the gate realization.
• The proposal is efficient and simple because only a classical microwave pulse is needed, no matter how many qudits are involved, which significantly reduces experimental difficulty.
• In a nonresonant case, the tunable phase gate can be achieved readily, while under the resonant condition, a {\pi}-phase gate can be realized after a full cycle of Rabi oscillation where the gate speed is rather fast due to the resonant interaction.