(a) (b) (c) N cav P e g cav (2) π −π π/2 −π/2 0 β$_{c}$  z FIG. 7: Same as Fig. 4 except for the detuning Δ$_{c}$ = 30 MHz. detuning of the probe field. To see the contrast between the case of exact resonance and the case of substantial detuning, we plot in Figs. 6 and 7 the results of the numerical calculations for the case where Δ$_{c}$ = 30 MHz. Figure 6(a) shows that, when r − a is large, N$_{cav}$ increases with decreasing r − a . In this region, the presence of the atom increases the number of intracavity photons. Figure 7(a) shows that the number of intracavity photons is largest when the atom is positioned at an antinode of the guided cavity field. Figures 6(b) and 7(b) show that, outside the nodes of the cavity standing-wave field, we have g (2) cav < 1, that is, the photon statistics is sub-Poissonian. Comparison between Figs. 3 and 6 and between Figs. 4 and 7 shows that the two cases have very different behaviors. r - a  [nm] (a) (b) (c) N cav P e g cav (2) FIG. 8: Same as Fig. 3 except for the cavity length L = 1 mm. According to Eq. (33), the atom can significantly affect the guided cavity field if the condi- 18