Unified generation and fast emission of arbitrary single-photon multimode W states

We propose a unified and deterministic scheme to generate arbitrary single-photon multimode W states in circuit QED. A three-level system (qutrit) is driven by a pump-laser pulse and coupled to N spatially separated resonators. The coupling strength for each spatial mode g_i totally decide the generated single-photon N-mode W state vert W_N rangle=frac{1}{A}sum_i=1^N g_i|0₁ 0₂ cdots 1_i 0_i+1cdots 0_Nrangle, so arbitrary vert W_N rangle can be generated just by tuning g_i. We could not only generate W states inside resonators but also release them into transmission lines on demand. The time and fidelity for generating (or emitting) vert W_N rangle can both be the same for arbitrary N. Remarkably, vert W_Nrangle can be emitted with probability reaching 98.9\% in 20-50 ns depending on parameters, comparable to the recently reported fastest two-qubit gate (30-45 ns). Finally, the time evolution process is convenient to control since only the pump pulse is time-dependent.