Two-qubit and three-qubit controlled gates with cross-Kerr nonlinearity

Schemes for two-qubit and three-qubit controlled gates based on cross-Kerr nonlinearity are proposed in this paper. The success probability of these gates can be increased by the quantum nondemolition detectors which are used to judge which paths the signal photons pass through. These schemes are nearly deterministic and require no ancilla photon. The advantages of these gates over the existing ones include Less resource consumption and higher success probability, which make our schemes more feasible with current technology.