Quantum

 In most contexts, “quantum” and “quantum physics” are used interchangeably and refer to the same field of study. “Quantum mechanics,” “quantum theory,” and “quantum physics” all describe the branch of physics that deals with the behavior of matter and energy at the atomic and subatomic level.  When someone says “quantum” or “quantum physics,” they are generally referring to the study of the microscopic world and its unique properties, including wave-particle duality, quantization of energy, and uncertainty.