Quantum system Schmidt decomposition and its geometric analysis

Quantum entangled state and some common methods to measure entanglement are introduced, and Schmidt decomposition of 2-qubit quantum state and the method to identify the entangled state are induced. A method to calculate the degree of entanglement is also given, which is obtained very easily by using the Schmidt decomposition. An example about NMR quantum computation is discussed to illustrate the application of the Schmidt decomposition. The evolution of the state of sub-system is described by using the Bloch vector, which demonstrates the geometric prospect of quantum system.