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As part of a project I'm working on, I want to use VQE algorithm to calculate the minimal eigenvalue for given Hamiltonian. I use Qiskit on IBM UI online.

The Hamiltonian is given as a sum of tensor products

$H = Z\otimes Z + Z \otimes X + ...$

I don't understand two main points:

  1. How should I pass the Hamiltonian to the VQE? should I pass it as a list? i.e. $ H = [Z\^Z, X\^Z]$?
  2. I understand that I need to create N circuits, where N is the number of tensor products which constitute the Hamiltonian, so that each circuit will handle another part of the Hamiltonian. Do I understand this correctly?

Thank you.

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Try this:

from qiskit.aqua.operators import WeightedPauliOperator
dict = {
    'paulis': [{"coeff": {"imag": 0.00, "real": 1 }, "label": "ZZ" },
              {"coeff": {"imag": 0.00, "real": 1 }, "label": "XX" }
              ]
}
Operator = WeightedPauliOperator.from_dict(dict)

Now you can pass this operator to your VQE call:

VQE(operator= Operator, var_form= ... )
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  • $\begingroup$ Thank you for your comment. After few trials it appears that the expression doesn't need to be modified but needs to be passed as it is $\endgroup$ – user14092875 Oct 15 '20 at 4:48
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After few trials, appears that VQE knows how to process this form of expression, so I just passed the mathematical expression as it is.

Thank you

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