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In physics, Berry connection and Berry curvature are related concepts, which can be viewed, respectively, as a local gauge potential and gauge field associated with the Berry phase. These concepts were introduced by Michael Berry in a paper published in 1984〔 〕 emphasizing how geometric phases provide a powerful unifying concept in several branches of classical and quantum physics. Such phases have come to be known as Berry phases. ==Berry phase and cyclic adiabatic evolution== In quantum mechanics, the Berry phase arises in a cyclic adiabatic evolution. The quantum adiabatic theorem applies to a system whose Hamiltonian depends on a (vector) parameter that varies with time . If the 'th eigenvalue remains non-degenerate everywhere along the path and the variation with time ''t'' is sufficiently slow, then a system initially in the eigenstate will remain in an instantaneous eigenstate of the Hamiltonian , up to a phase, throughout the process. Regarding the phase, the state at time ''t'' can be written as〔 〕 : where the second exponential term is the "dynamic phase factor." The first exponential term is the geometric term, with being the Berry phase. By plugging into the time-dependent Schrödinger equation, it can be shown that : indicating that the Berry phase only depends on the path in the parameter space, not on the rate at which the path is traversed. In the case of a cyclic evolution around a closed path such that , the closed-path Berry phase is : An example of physical system where an electron moves along a closed path is cyclotron motion (details are given in the page of Berry phase). Berry phase must be considered to obtain the correct quantization condition. 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「Berry connection and curvature」の詳細全文を読む スポンサード リンク
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