TeNPy Forum

I have written code which uses dmrg to find the ground state MPS of a Bose-Hubbard system. It is easy enough to extract the density distribution and correlators from this, using But I am interested in extracting the momentum distribution of the resulting state. I can use expectation_value('P') to get a site-by-site magnitude, however what I am really interested in is a full 2D resolved distribution of the momentum of the state. In particular, I am interested in seeing the coherent momentum peaks in a superfluid state.

I am curious if this is something which is possible, straightforward or not, in the MPS-style formalism, since my searches so far have come up fairly empty. I would welcome any advice, papers, or directions in which to look.

I'm not quite sure what you mean with "momentum distribution".
What you can do is measure the correlation function corrs=psi.correlation_function('bd', b') to get \(\bra{\psi} b^\dagger_i b_{j} \ket{\psi}\) in real space, and then perform a fourier trafo on both axes, which gives you something like \(\bra{\psi} b^\dagger_k b_{k'} \ket{\psi}\) with \(b_k = sum_j \exp(i j k) b_j\).
For that to make sense, you however need to think wether the Fourier trafo is actually well defined and physically sensible, i.e. whether those b_k still fulfill the commutation relations you expect, and whether k is a good quantum number - with MPS, we usually consider open systems at least in x-direction, where this is not the case!