Bogoliubov transformation 3-mode

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Discussion Overview

The discussion revolves around the application of the Bogoliubov transformation in the context of spin-wave theory, specifically focusing on the transformation involving three bosonic operators. Participants explore the existence and formulation of such a transformation, as well as its implications in Hamiltonians with non-diagonal terms.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses difficulty in finding a Bogoliubov transformation for three bosons, having only encountered formulations for one and two bosons.
  • Another participant requests the Hamiltonian to better understand the context of the problem.
  • A participant describes their Hamiltonian, which includes products of boson operators and emphasizes the need for a transformation to diagonalize it.
  • One participant asserts that a solution exists for the fermionic case, suggesting that similar methods may apply to bosons, although they do not provide the specific solution.
  • Another participant speculates that the transformation for fermions might not differ significantly from that for bosons, expressing hope for a similar approach.
  • A later reply suggests a method to express the Hamiltonian in terms of a vector and a matrix, proposing a way to diagonalize it through a unitary transformation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the specific form of the Bogoliubov transformation for three bosons, and multiple viewpoints regarding its existence and formulation remain present.

Contextual Notes

The discussion highlights the complexity of the Hamiltonian involved and the challenges posed by non-diagonal terms, which may affect the formulation of the transformation. There is also an acknowledgment of the potential differences between bosonic and fermionic transformations.

Naibaf
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Hi everyone,

I'm working on spin-wave theory and I have a problem with a bogoliubov transformation.
I must do the transformation with 3 bosons and i have no idea how to do it.
I've only found the transformation for 1 and 2-mode bosons, but not for three...

It exist?

Thanks...



And sorry for my english...
 
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Maybe you could provide us with your hamiltonian?
 
The hamiltonian is very long, but the idea is that I have, products of bosons operator, for example: a*a + a*b + a*c + b*b + bb + b*c and so on...

Where a, b an c are boson operators.
As there are "non-diagonal" terms, the idea is use Bogoliubov Transformation for make the hamiltonian a diagonal hamiltonian... But for 2 differents bosons, the tranformation is:

alpha_{k} = cosh(theta_{k}) a_{k} - sinh(theta_{k}) b*_{k}, where b* is b-dagger

ans this transformation is like "universal" because everyone use it.
So my question is if there is a known bogoliubov transformation for 3 differents bosons in a hamiltonian...
( I hope you understand my english :) )
 
I can certainly tell you that a solution exists, at least in the fermionic case, because the Bogoliubov transformation is used routinely in nuclear physics, where you can have ~100 protons and neutrons. Sorry not to be able to supply the actual solution you want :-)
 
In this case, the 3 bosons operators are different, I have: a, b and c.
I guess that for ~100 differents protons the transformation must be huge!

I also guess that the bogoliubov transformation for fermions should not be so different from that of bosons......at least I have some hope! :)
thanks
 
So, introducing the vector [tex]A=(a_k, a^*_{-k}, b_k, b^*_{-k},c_k, c^*_{-k})^T[/tex],
you should be able to write your hamiltonian as [tex]H=A^\dagger M(k) A[/tex]. Then you have to find the unitary transformation U which diagonalizes the matrix M, i.e., you have to solve the eigenvalue problem for M. Then the vector of the alphas is UA.
Not a big deal, in principle.
 

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