Squeezed vacuum, as a nonclassical field, has many interesting properties and results in many potential applications for quantum measurement and information processing. Here, we investigate a single atom–cavity quantum electrodynamics (QED) system driven by a broadband squeezed vacuum. In the presence of the atom, we show that both the mean photon number and the quantum fluctuations of photons in the cavity undergo a significant depletion due to the additional transition pathways generated by the atom–cavity interaction. By measuring these features, one can detect the existence of atoms in the cavity. We also show that two-photon excitation can be significantly suppressed by the quantum destructive interference when the squeezing parameter is very small. These results presented here are helpful in understanding the quantum nature of the broadband squeezed vacuum.