There has been wide interest in splitter, quantum tunneling, and double-slit experiments for a long time. The states of single material particles are typically explained as being independent of other objects (and/or electromagnetic fields) and interactions. This independence causes counterintuitive explanations. By analyzing the research conducted separately by Wineland's group and Haroche's group, we naturally deduced that the states are dependent on other objects. Based on this dependence, our unified explanation is more intuitive. We design a double-slit thought experiment that can solve the center problem, i.e., which-path information. The dependence can also work for qubits in quantum information. To emphasize and use the dependence in the future, we propose a fundamental postulate that no material particle is free as the zeroth postulate of quantum mechanics.