by a superconducting transmission line for a quantum network. They are implemented with coherent evolutions of the entire system in the all-resonance regime assisted by the dark microwave photons which are robust against the transmission line loss. Different from previous works in other quantum systems for a quantum network, the present proposals do not require classical pulses and ancillary qubits. Our simulations with feasible parameters show that the fidelities of both these schemes exceed 99% which is beyond the fault-tolerant threshold for quantum communication.

in previous works with some resonators coupled to a superconducting qubit (SQ), our device is composed of some 1D SRs rj which are coupled to the quantum bus (another common resonator R) in its different positions simply, assisted by superconducting quantum interferometer devices. By using the technique for catching and releasing a MP state in a 1D SR, it can work as an entanglement generator or a node in quantum communication. To demonstrate the performance of this device, we propose a one-step scheme to generate high-fidelity Bell states on MPs in two distant SRs. It works in the dispersive regime of rj and R, which enables us to extend it to generate high-fidelity multi-Bell states on different resonator pairs simultaneously.

that is, the resonant operation on the qutrit and the resonator, and the single-qubit operation on the qutrit, and they both are high-fidelity operations. Compared with the one by a superconducting transmon qutrit proposed by Su et al. (Sci. Rep. 4, 3898 (2014)), our scheme does not require to maintain the qutrit in the third excited state with a long time, which relaxes the difficulty of its implementation in experiment. Moreover, the level anharmonicity of a charge qutrit is larger and it is better for us to tune the different transitions of the charge qutrit resonant to the resonator, which makes our scheme faster than others.

of some resonators coupled to a superconducting qubit, our processor is composed of some resonators ri and a common resonator R acting as a quantum bus, which makes it have the capability of integrating more resonators simply by coupling them to the bus R in different positions. R is coupled to only one transmon qutrit, and the coupling strengths between ri and R can be fully tuned. To show the processor can be used to achieve universal quantum computation effectively, we present a scheme to complete the high-fidelity quantum state transfer between two microwave-photon resonators and another one for the high-fidelity controlled-phase gate on them.

previous works. It is a second-order coupling effect between the resonator and the qubit in the dispersive regime, which leads to a long-time state-selective rotation on the qubit. Here, we use the quantum resonance operations to construct the fast universal quantum gates on superconducting resonators in a microwave-photon quantum processor composed of some superconducting resonators coupled to a superconducting transmon, phase, or Xmon qutrit assisted by circuit QED in the dispersive regime, including the controlled-phase (c-phase) gate on two microwave-photon resonators and the controlled-controlled phase (cc-phase) gates on three microwave-photon resonators. Compared with previous works, our universal quantum gates have the higher fidelities and shorter operation times. The fidelity of our c-phase gate is 98.7% within the operation time of 40.1 ns and that of our cc-phase gate is 94.7% within 60 ns. Moreover, they do not require any drive field.

and controlled-controlled-phase (cc-phase) gates on microwave-photon-resonator qudits, by combination of the photon-number-dependent frequency-shift effect and the resonant operation between the qutrit and a resonator. This distinct feature provides us a useful way for achieving higher fidelity quantum logic gates on resonator qudits in a shorter operation time, compared with others. The fidelity of our c-phase gate can reach 99.51% within 92 ns. The fidelity of our cc-phase gate on three resonator qudits constructed here in the first time, can reach 92.92% within 124.64 ns.