Starting Initial State as product state of singlets

+1 vote
asked May 4 by Dhiman (150 points)

Is there any way to construct the initial state so that it will be a product state of singlets??
For example if I have 2N sites I want N singlets to initialize the state.

1 Answer

0 votes
answered May 7 by miles (18,230 points)

Hi Dhiman,
Good question as this is an important thing to be able to do sometimes. And of course you can do this, yes, as one can set the elements of an ITensor or IQTensor individually so you can make any MPS this way.

Here is a sample code that makes an MPS which is a product state of singlets. To do the IQMPS version all you should need to do is change MPS to IQMPS and ITensor to IQTensor.

auto psi = MPS(sites);
for(int n = 1; n <= 2*N; n += 2)
    {
    auto s1 = sites(n);
    auto s2 = sites(n+1);
    auto wf = ITensor(s1,s2);
    wf.set(s1(1),s2(2), ISqrt2);
    wf.set(s1(2),s2(1), -ISqrt2);
    ITensor D;
    psi.Aref(n) = ITensor(s1);
    psi.Aref(n+1) = ITensor(s2);
    svd(wf,psi.Aref(n),D,psi.Aref(n+1));
    psi.Aref(n) *= D;
    }
commented May 10 by Dhiman (150 points)
Thanks miles.
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