In a nutshell, quantum refers to the principles and phenomena that govern the behavior of matter and energy at extremely small scales, such as atoms and subatomic particles. It is a branch of physics known as quantum mechanics or quantum physics.
Classical physics describes the world around us in terms of continuous variables and predictable cause-and-effect relationships. However, at the quantum level, particles can exhibit strange behaviors that defy classical intuition. These behaviors include superposition and entanglement.
Superposition is the ability of particles to exist in multiple states simultaneously. For example, a subatomic particle like an electron can be in a superposition of being in different places or having different properties at the same time. It is only when the particle is measured that it "collapses" into a definite state.
Entanglement, on the other hand, is a phenomenon where two or more particles become linked in such a way that the state of one particle is instantaneously connected to the state of the other(s), regardless of the distance between them. This connection persists even if the particles are separated by vast distances.
Quantum mechanics also introduces the concept of quantized energy levels, where energy is "quantized" into discrete units called quanta. This leads to phenomena like the wave-particle duality, where particles can exhibit both wave-like and particle-like properties.
Quantum mechanics has numerous practical applications, including quantum computing, cryptography, and precision measurements. It has revolutionized our understanding of the microscopic world and continues to push the boundaries of scientific exploration and technological advancements.