Entangling homogeneously broadened matter qubits in the weak-coupling cavity-QED regime

In distributed quantum information processing, flying photons entangle matter qubits confined in cavities. However, when a matter qubit is homogeneously broadened, the strong-coupling regime of cavity QED is typically required, which is hard to realize in actual experimental setups. Here, we show that a high-fidelity entanglement operation is possible even in the weak-coupling regime in which dampings (dephasing, spontaneous emission, and cavity leakage) overwhelm the coherent coupling between a qubit and the cavity. Our proposal enables distributed quantum information processing to be performed using much less demanding technology than previously

Deterministic photon-photon (SWAP)^{1/2} gate using a lambda system

We theoretically present a method to realize a deterministic photon-photon (SWAP)^{1/2} gate using a three-level lambda system interacting with single photons in reflection geometry. The lambda system is used completely passively as a temporary memory for a photonic qubit; the initial state of the lambda system may be arbitrary, and active control by auxiliary fields is unnecessary throughout the gate operations. These distinct merits make this entangling gate suitable for deterministic and scalable quantum computation.Comment: 7 pages, 4 figure

Efficient numerical approach for the simulations of high-power dispersive readout with time-dependent unitary transformation

We develop an efficient numerical approach for simulating the high-power dispersive readout in circuit quantum electrodynamics. In the numerical simulations of the high-power readout, a large-amplitude coherent state induced in a cavity is an obstacle because many Fock states are required to describe such a state. We remove the large-amplitude coherent state from the numerical simulations by simulating the dynamics in a frame where the amplitude of the coherent state is almost absent. Using the developed method, we numerically simulate the high-power dispersive readout of the two-level system and the transmon. Our proposed method succeeds in producing reasonable behaviors of the high-power dispersive readout which can be deduced from the photon-number dependence of the cavity frequency: The high-power dispersive readout works in the two-level-system case while it does not work in the transmon case.Comment: 11 pages, 10 figures, accepted versio