Hello all,
I am learning how to use the ALPS applications. I had reasonable success with DMRG with which I am experienced, however I was trying to study two dimensional systems with QMC and I ran into a problem: The ALPS application complains that it will not measure off-diagonal observables such as sigma_x, even less for two operators like sigma^plus_i sigma^minus_j. It measures without any problems sigma_z and correlations of sigma_z operators.
Now, my ignorance of QMC is such that I don't know if this is an intrinsic limitation of Quantum Montecarlo algorithms or just of the particular example application distributed with ALPS -- this is my first question. My second question is: if it is possible to measure e.g. sigma_x, could you give me a rough estimate of how difficult could it be to implement it with the libraries?
Thanks in advance,
Fernando Cucchietti