Quantum Systems refers to a branch of physics that deals with physical phenomena at very small scales, such as atomic and subatomic levels. In this realm, classical mechanics no longer apply, and instead we encounter quantum mechanical behavior - where particles exist in multiple states simultaneously (superposition) and can only be described by probabilities rather than definite outcomes. This field of study is essential for understanding the fundamental nature of matter and energy, as well as many technological applications such as quantum computing, cryptography, and advanced materials science.