Relativistic Single Particle Quantum Mechanics

The Dirac equation is usually taught to undergraduates in physics as the foundation of relativistic quantum mechanics. It describes very well the behavior of single particles in a purely quadratic potential, an even potential, to the ends that second quantization becomes evident. This means that particles appear. Particles are useful because they are inherently physical and intuitive. The "interaction quantum" was proposed in some of the literature I have been reading and it is the focus of my strategic advisement in quantum systems, where the interaction energy or the observational energy is a small amount of destabilizing energy (decoherence) that limits the lifetime of stable qubits.