翻訳と辞書 Words near each other ・ Quantum relative entropy ・ Quantum revival ・ Quantum rotor model ・ Quantum satis ・ Quantum sensor ・ Quantum Sheep ・ Quantum simulator ・ Quantum singularity ・ Quantum solid ・ Quantum solvent ・ Quantum sort ・ Quantum spacetime ・ Quantum spin Hall effect ・ Quantum spin liquid ・ Quantum spin model ・ Quantum spin tunneling ・ Quantum Sports Cars ・ Quantum state ・ Quantum statistical mechanics ・ Quantum stirring, ratchets, and pumping ・ Quantum stochastic calculus ・ Quantum suicide and immortality ・ Quantum suicide and quantum immortality in fiction ・ Quantum superposition ・ Quantum system ・ Quantum t-design ・ Quantum technology ・ Quantum teleportation ・ Quantum Theatre ・ Quantum Theology Dictionary Lists mini英和辞書 mini和英辞書 Webster 1913 Latin-English FOLDOC Wikipedia English ウィキペディア

翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Quantum spin tunneling ： ウィキペディア英語版 Quantum spin tunneling Quantum spin tunneling, or quantum tunneling of magnetization, is a physical phenomena by which the quantum mechanical state that describes the collective magnetization of a nanomagnet is a linear superposition of two states with well defined and opposite magnetization. Classically, the magnetic anisotropy favors either of the two states with opposite magnetization, so that the system has two equivalent ground states. Because of the quantum spin tunneling, an energy splitting between the bonding and anti-bonding linear combination of states with opposite magnetization classical ground states arises, giving rise to a unique ground state separated by the first excited state by an energy difference known as quantum spin tunneling splitting. The quantum spin tunneling splitting also occurs for pairs of excited states with opposite magnetization. As a consequence of quantum spin tunneling, the magnetization of a system can switch between states with opposite magnetization that are separated by an energy barrier much larger than thermal energy. Thus, quantum spin tunneling provides a pathway to magnetization switching forbidden in classical physics. Whereas quantum spin tunneling shares some properties with quantum tunneling in other two level systems such as a single electron in a double quantum well or in a diatomic molecule, it is a multi-electron phenomena, since more than one electron is required to have magnetic anisotropy. The multi-electron character is also revealed by an important feature, absent in single-electron tunneling: zero field quantum spin tunneling splitting is only possible for integer spins, and is certainly absent for half-integer spins, as ensured by Kramers degeneracy theorem. Initially discussed in the context of magnetization dynamics of magnetic nanoparticles, the concept was known as macroscopic quantum tunneling, a term that highlights both the difference with single electron tunneling and connects this phenomenon with other macroscopic quantum phenomena. In this sense, the problem of quantum spin tunneling lies in the boundary between the quantum and classical descriptions of reality. == Single spin Hamiltonian == A simple single spin Hamiltonian that describes quantum spin tunneling for a spin $S$ is given by: $\backslash hat=\; D\backslash hat\_z^2\; +\; E\; (\backslash hat\_x^2\; -\backslash hat\_y^2)$ () where ''D'' and ''E'' are parameters that determine the magnetic anisotropy, and $\backslash hat\_x,\; \backslash hat\_y,\; \backslash hat\_z$ are spin matrices of dimension $2S+1$ . It is customary to take z as the easy axis so tha''t D<0'' and ''|D|>> E''. For E=0, this Hamiltonian commutes with $\backslash hat\_z$ , so that we can write the eigenvalues as $E(S\_z)=\; DS\_z^2$, where $S\_z$ takes the ''2S+1'' values in the list ''(S, S-1, ...., -S)'' escribes a set of doublets, with $E=0$ and . In the case of integer spins the second term of the Hamiltonian results in the splitting of the otherwise degenerate ground state doublet. In this case, the zero field quantum spin tunneling splitting is given by: $\backslash Delta\; \backslash propto\; E\; \backslash left(\backslash frac\backslash right)^$ From this result, it is apparent that, given that E/D is much smaller than 1 by construction, the quantum spin tunnelling splitting becomes suppressed in the limit of large spin S, ie, as we move from the atomic scale towards the macroscopic world. Interestingly, the magnitude of the quantum spin tunnelling splitting can be modulated by application of a magnetic field along the transverse hard axis direction (in the case of Hamiltonian (), with D<0 and E>0, the x axis). The modulation of the quantum spin tunnelling splitting results in oscillations of its magnitude, including specific values of the transverse field at which the splitting vanishes. This accidental degeneracies are known as diabolic points. 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「Quantum spin tunneling」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.