How to calculate asymmetric atomic fluorescence spectrum

[zhihu...@gmail.com]

Dear all,

 The normal way to calculate the symmetric fluorescence spectrum is write the Hamiltonian, set the time list from 0 to certain time T and use function "correlation_2op_1t" and function "spectrum_correlation_fft". However, I need to calculate asymmetric atomic fluorescence spectrum. It seems I have to set the time from -T to T. Unfortunately, the function  "correlation_2op_1t" and  "spectrum_correlation_fft" don't support the negative time. How can I realize the calculation with Qutip?

Best regards,

Zhihui

[Andrew Dawes]

Can you say more about what you mean by asymmetric spectrum? Is that a particular calculation or are you calculating the spectrum for a Hamiltonian where you expect to see an asymmetric spectrum? I ask because it seems like the physics shouldn’t change simply by shifting the time origin.

Andy

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[zhihu...@gmail.com]

Dear Andrew,

I mean it usually assume the fluorescence spectrum is symmetric about the center frequency and it is enough calculate the positive branch related to center frequency. However, if we have to calculate both positive branch and negative branch related to the center frequency in a particular case, I cannot use qutip do that. 

Best,

Zhihui

[Andrew Dawes]

Zhihui,

I understand that interpretation of the spectrum calculation. There are two methods in QuTiP, one uses the FFT and returns only the positive-time portion, the other uses the semi-analytical transform and returns values at a specific list of frequencies (which can be positive or negative). I’ve modified one of the QuTiP examples to illustrate what I mean:

https://gist.github.com/amcdawes/146a91f701be851ac94144bf67303f8f

also, please see the original documentation for QuTiP here: 

http://qutip.org/docs/latest/guide/guide-correlation.html?highlight=spectrum#emission-spectrum

and the rest of that page.

Best,

Andy

[zhihu...@gmail.com]

Dear Andrew,

Thank you very much for your help. I will try.

Best,

Zhihui