## Coherence

Topics related to Spinach package
NMR-trainee
Posts: 12
Joined: Tue May 24, 2022 6:32 am

### Coherence

Hi!

I have a problem with the phases of my spectrum. One way I received the correct spectrum was by a loop that takes multiple spectra with different amount of time steps and averages the spectrum by the number of total spectra.

But I think there is an easier way to solve this. And I think it could be done by removing coherences. So how can I extract populations and coherences separately? Meaning the diagonal and undiagonal elements of the density matrix. Is there maybe a function for this? I thought that coherence.m and/or correlation.m could be used, but it seems that coherence - and correlation orders are a different thing.

Once again, many thanks.
kuprov
Posts: 125
Joined: Mon Mar 29, 2021 4:26 pm

### Re: Coherence

Well, yes, coherence() and correlation() filter specific coherence and correlation orders.

https://spindynamics.org/wiki/index.php ... oherence.m
https://spindynamics.org/wiki/index.php ... relation.m

The difference is that coherence order is an eigenstate of the total Lz operator with a particular multiple of the frequency, and correlation order is the number of non-unit Pauli matrices in the direct product state.
NMR-trainee
Posts: 12
Joined: Tue May 24, 2022 6:32 am

### Re: Coherence

Thank you for the answer, I might have been a bit unspecific in my first question.

Is there a way to extract populations and coherences, diagonal and off-diagonal, of the density matrix in the eigenbasis of the hamiltonian?
kuprov
Posts: 125
Joined: Mon Mar 29, 2021 4:26 pm

### Re: Coherence

Well, sure - choose Hilbert space as formalism, get the Hamiltonian, diagonalise it, transform your density matrix into its eigenframe, and just use Matlab indexing to extract the elements of the matrix.