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In physics, an open quantum system is a quantum-mechanical system which interacts with an external quantum system, the ''environment''. In reality, no quantum system is completely isolated from its surroundings, so every quantum system is open to some extent, causing dissipation in the quantum system. Techniques developed in the context of open quantum systems have proven powerful in fields such as quantum optics, quantum measurement theory, quantum statistical mechanics, quantum information science, quantum cosmology and semi-classical approximations. The environment we wish to model as part of our open quantum system is typically very large, making exact solutions impossible to calculate. However, by making key approximations it is possible to find out how the quantum system behaves in the presence of the environment. There are two approximations commonly made in the field of open quantum systems: the Born approximation and the Markov approximation. The Born approximation assumes that the system-bath coupling is relatively weak, and the bath is very large, so that the bath is negligibly affected by the system. The Markov approximation assumes that the bath has no memory of past events. ==See also== * * Lindblad equation * Markov property * Master equation 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「open quantum system」の詳細全文を読む スポンサード リンク
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