Entanglement Generation by a Scattering Process with a Moving Particle

In a scalable quantum computer, it is very important to make the two-qubit gate generating the entangled state for a pair of qubits spatially separated from each other. We propose a method to entangle qubits that stand apart from each other. The initial separable state of two far-distanced particles evolves into a maximally entangled state by controlling the interaction time with an auxiliary moving particle. This implies that one can construct a two-qubit gate (CNOT gate) for a pair of particles separated far apart. Furthermore, we show that N qubits prepared initially as a separable state can become a W-state through the same interactions as in the two-qubit case.