Figure 3: Comparison with classical light and entanglement entropy.

(a) Two-exciton state distributions induced by the absorption of entangled photon pairs (bottom), chirped pulses (middle) and stochastic light (top) with T=10 fs, and σ_p=100 cm⁻¹. The central frequency of beam 2 is fixed at ω₂=11,000 cm⁻¹, while ω₁ is varied. The two previously mentioned states f₁₁ and f₂₃ are highlighted. (b) The same for T=100 fs, and σ_p=400 cm⁻¹. (c) The population of state f₂₃ versus the pump bandwidth σ_p with ω₁=11,908.3 cm⁻¹ and ω₂=12,200 cm⁻¹. Population created by entangled photons is plotted in red, classical pulses in blue. (d) Entanglement entropy of the two-photon state (5) versus the entanglement time T and the pump bandwidth σ_p. The area, for which (1) is violated, is separated by a red line, and the parameters of figures (a,b) are indicated.