  This paper studies the effect of single-photon light fields on quantum
entanglement between two qubits and multiple identical qubits initially in a
direct state. For two qubits, we first analyze the impact of the excited
state's weight on single-photon-triggered entanglement, finding that excessive
weight disrupts this process. We then explore how initial coherence affects
entanglement, discovering that maximum initial coherence enables the single
photon to achieve maximal entanglement. For multiple qubits, we similarly
investigate the effects of the excited state's weight and initial coherence on
entanglement control. In large qubit systems, we find that single photons
cannot trigger entanglement when excited-state weights exceed ground-state
weights or when all qubits are initially in the ground state. Interestingly,
single photons can still trigger entanglement between any two qubits in systems
with at least 2000 qubits, with the entanglement depending on initial state
parameters rather than the number of qubits.
