Absorption and emission spectrum in quantum optics

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Discussion Overview

The discussion revolves around the emission and absorption spectra in quantum optics, particularly focusing on quantum dots, atoms, and defect centers. Participants explore the mathematical formulations related to resonance fluorescence and inquire about the absorption spectrum, including the effects of coupling to local vibrational modes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant references multiple quantum optics textbooks that discuss the emission spectrum and provides a specific formula for resonance fluorescence.
  • A question is raised regarding the formula for the absorption spectrum and its relation to systems coupled to local vibrational modes, such as polarons.
  • Another participant mentions a review paper that discusses spectral line shapes, indicating that both absorption coefficients and emissivities can be expressed in terms of Fourier transforms of the dipole moment auto-correlation function.
  • A further inquiry is made about the availability of this information in spectroscopy texts, particularly those that are quantum mechanical rather than semiclassical.
  • One participant introduces the concept of linear-response theory and the Green-Kubo formula as it relates to the autocorrelation function of the source.
  • A participant expresses gratitude for finding additional resources that provide a broader context for the discussion.

Areas of Agreement / Disagreement

Participants express varying levels of familiarity with the topic, and while some references are shared, there is no consensus on the specifics of the absorption spectrum or its mathematical formulation. Multiple competing views and questions remain unresolved.

Contextual Notes

Participants note the dependence on definitions and the potential limitations of introductory texts in providing a comprehensive understanding of the topics discussed.

Cedric Chia
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TL;DR
Absorption spectrum for a quantum dot
The emission spectrum or resonance fluorescence for a quantum dot, atom or defect center are discussed in many quantum optics textbook, for example see "Quantum Optics" by Marlan O. Scully and M. Suhail Zubairy Chapter 10 , "Quantum Optics" by D. F. Walls and Gerard J. Milburn Chapter 10 and "Quantum Optics" by Raymond Chiao and John Garrison Chapter 14.

In these textbooks, the formula for resonance fluorescence is given by:
$$
\alpha(\omega)=Re\int_0^{\infty}dt\left<E^{(-)}(t)E^{(+)}(t+\tau)\right>e^{i\omega\tau}
$$
where one usually relates the electric field operator with the atomic raising/lowering operator:
$$
\left<E^{(+)}(t)\right>\propto\left<\sigma\right>
$$

But what about the formula for absorption spectrum? Where can I find discussion on the absorption spectrum? And what if I have a system coupled to local vibrational modes (a polaron), how would that change the formula of emission and absorption spectrum?
 
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I know very little about quantum dots, but I do remember a review paper on spectral line shapes: van Vleck J H and Huber D L 1977, Rev. Mod. Phys. 49, 939-959. Both, absorption coefficients and emissivities can be expressed in terms of Fourier transforms of the dipole moment auto-correlation function, or more generally, of the current density fluctuations.
 
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WernerQH said:
spectral line shapes: van Vleck J H and Huber D L 1977, Rev. Mod. Phys. 49, 939-959. Both, absorption coefficients and emissivities can be expressed in terms of Fourier transforms of the dipole moment auto-correlation function, or more generally, of the current density fluctuations.
Is this not found in spectroscopy texts/monographs (or at least rather quantum mechanical ones as opposed to semiclassical)?
 
That's a very general basic principle. In linear-response theory the response function is given in terms of the (retarded) autocorrelation function of the source. It's also known as the Green-Kubo formula.
 
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