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Concept
Bogoliubov transformation
Résumé
In theoretical physics, the Bogoliubov transformation, also known as the Bogoliubov–Valatin transformation, was independently developed in 1958 by Nikolay Bogolyubov and John George Valatin for finding solutions of BCS theory in a homogeneous system. The Bogoliubov transformation is an isomorphism of either the canonical commutation relation algebra or canonical anticommutation relation algebra. This induces an autoequivalence on the respective representations. The Bogoliubov transformation is often used to diagonalize Hamiltonians, which yields the stationary solutions of the corresponding Schrödinger equation. The Bogoliubov transformation is also important for understanding the Unruh effect, Hawking radiation, pairing effects in nuclear physics, and many other topics.
The Bogoliubov transformation is often used to diagonalize Hamiltonians, with a corresponding transformation of the state function. Operator eigenvalues calculated with the diagonalized Hamiltonian on the transformed state function thus are the same as before.
Consider the canonical commutation relation for bosonic creation and annihilation operators in the harmonic basis
Define a new pair of operators
for complex numbers u and v, where the latter is the Hermitian conjugate of the first.
The Bogoliubov transformation is the canonical transformation mapping the operators and to and . To find the conditions on the constants u and v such that the transformation is canonical, the commutator is evaluated, namely,
It is then evident that is the condition for which the transformation is canonical.
Since the form of this condition is suggestive of the hyperbolic identity
the constants u and v can be readily parametrized as
This is interpreted as a linear symplectic transformation of the phase space. By comparing to the Bloch–Messiah decomposition, the two angles and correspond to the orthogonal symplectic transformations (i.e., rotations) and the squeezing factor corresponds to the diagonal transformation.
The most prominent application is by Nikolai Bogoliubov himself in the context of superfluidity.
Source officielle
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