Dear Michael,
Could you try defining the operator c_up(x)*bdag(x) as a SITEOPERATOR and use it in the BONDOPERATOR? Or even defining it in the basis.
Best, Michele
-- ETH Zurich Michele Dolfi Institute for Theoretical Physics HIT G 32.4 Wolfgang-Pauli-Str. 27 8093 Zurich Switzerland
dolfim@phys.ethz.ch www.itp.phys.ethz.ch
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On Feb 6, 2016, at 2:08 PM, Michael Pasek michael.pasek@univ-paris-diderot.fr wrote:
Dear all,
I am trying to compute the correlation of two bond operators as follows:
p['MEASURE_CORRELATIONS[custom op]'] = 'cppdag:cpp'
where cpp and cppdag are define in mymodel.xml as:
<BONDOPERATOR name="cpp" source="x" target="y"> c_up(x)*bdag(x)*c_up(y)*bdag(y) </BONDOPERATOR> <BONDOPERATOR name="cppdag" source="x" target="y"> b(x)*cdag_up(x)*b(y)*cdag_up(y) </BONDOPERATOR>
where bdag, b, cdag_up and c_up are the usual boson, fermion creation-annihilation operators. Disappointingly, in this case mps_optim only outputs a single number for the correlation measurement.
If I try instead to compute the correlation 'oppdag:opp' with
<BONDOPERATOR name="opp" source="x" target="y"> bdag(x)*c_up(y) </BONDOPERATOR> <BONDOPERATOR name="oppdag" source="x" target="y"> cdag_up(x)*b(y) </BONDOPERATOR>
... I get a 4x4 matrix (i,i+1,j,j+1) as expected. So the problem seems to come from computing the correlation of bond operators that are products of more than two site operators.
Is this measurement expected to fail with mps_optim, or am I doing something wrong?
Thank you for your help.
Michael