Quantum computing is computing using quantum-mechanical phenomena, such as superposition and entanglement. This is the principle of quantum superposition. A quantum walk can be described by a quantum superposition over states. A mixed state is different from a quantum superposition. An entangled state is a linear superposition of separable states. Entanglement is a basis-independent result of superposition. The superposition theorem is very important in circuit analysis. Linear control theory applies to systems made of devices which obey the superposition principle. This is the principle of linear superposition in probability. This can be reduced to a simple dipole using the superposition principle. This was followed by the first experimental realization of coherent spin superposition of matter waves. Linear systems satisfy the property of superposition. This superposition or linear combination is called the Fourier series. This power series expresses a function as a linear superposition of moments of the function. This is usually the case in linear systems, when the superposition principle holds.