Has Hilbert transform ever been used in Quantum Theory?

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Discussion Overview

The discussion revolves around the application of the Hilbert transform in quantum theory (QT). Participants explore its potential uses in various contexts, including scattering theory and quantum control theory, while expressing uncertainty about its prevalence in standard quantum mechanics literature.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether the Hilbert transform has been directly used in quantum theory, noting its appearance in complex analysis and signal analysis courses.
  • Another participant mentions that in scattering theory, the Jost functions exhibit a relationship where the real and imaginary parts are Hilbert transforms of each other, suggesting a specific application of the transform.
  • A different participant recalls using the Hilbert transform in a perturbation expansion of a unitary operator, indicating a simpler approach compared to traditional methods, but does not provide details.
  • One participant reiterates the initial question about the Hilbert transform's use in QT and references the Kramers-Kronig relations in quantum optics, suggesting a broader application in the field.

Areas of Agreement / Disagreement

Participants express varying degrees of familiarity with the Hilbert transform's application in quantum theory, with no consensus on its overall usage or significance in the field. Multiple competing views and examples are presented without resolution.

Contextual Notes

Some participants reference specific contexts, such as scattering theory and quantum optics, but the discussion lacks detailed exploration of the assumptions or limitations related to the Hilbert transform's application in quantum theory.

mad mathematician
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Anyone knows if this transform ever been used in QT directly?

I just had seen it in one advanced course in complex analysis which I failed and in singals analysis courses in EE.
But in all the books and courses in QT never I had seen this transform being used.

Perhaps in Quantum Control theory...
https://en.wikipedia.org/wiki/Hilbert_transform
 
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In scattering theory, when you consider the so-called (complex-valued) Jost functions ##F_l(k)##, the dispersion relations relate the real and the imaginary parts of ##F_l(k) -1##. And the specific form of these relations make each the Hilbert transforms of the other. Just google for Jost functions and dispersion relations.
 
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I used it once in a perturbation expansion of a unitary operator. It was somewhat simpler than the usual expansion of the complex exponential. But I forgot the details.
 
mad mathematician said:
Anyone knows if this transform ever been used in QT directly?

I just had seen it in one advanced course in complex analysis which I failed and in singals analysis courses in EE.
But in all the books and courses in QT never I had seen this transform being used.

Perhaps in Quantum Control theory...
https://en.wikipedia.org/wiki/Hilbert_transform
The Kramers Kronig relations in (quantum) optics.

Edit: Looks like the KK relations are used for almost everything:
https://en.wikipedia.org/wiki/Kramers–Kronig_relations
 
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