Multilevel quantum coherence and its quantum-vacuum counterpart, where a three-level dark state is involved, are suggested in order to achieve new photonic and quantum optical applications. It is shown that such a three-level dark state in a four-level tripod-configuration atomic system consists of three lower levels, where constructive and destructive quantum interference between two control transitions (driven by two control fields) arises. We point out that the controllable optical response due to the double-control tunable quantum interference can be utilized to design some fascinating new photonic devices such as logic gates, photonic transistors and switches at quantum level. A single-photon two-input XOR logic gate (in which the incident “gate” photons are the individual light quanta of the two control fields) based on such an effect of optical switching control with an EIT (electromagnetically induced transparency) microcavity is suggested as an illustrative example of the application of the dark-state manipulation via the double-control quantum interference. The present work would open up possibility of new applications in both fundamental physics (e.g., field quantization and relevant quantum optical effects in artificial systems that can mimic atomic energy levels) and applied physics (e.g., photonic devices such as integrated optical circuits at quantum level).