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I am attempting to use a VQE algorithm to find the ground state of a deuterium nucleus by applying a constructed hamiltonian to an ansatz state with one parameter created by a circuit. While I am getting a different expectation value for different parameters, it does not line up with what I am supposed to get (from the paper I am attempting to replicate). I think the basis is wrong. How should I change the basis to fit the hamiltonian I am using? Should I change the basis of the hamiltonian (which I got from tensor products of pauli operators)? Or should I change the basis of the ansatz itself to fit that of the hamiltonian?

PS: this (arXiv link) is the paper whose results I am trying to replicate (The H2 graph to be specific). They are using ↑ and ↓ as their basis while I am still on qiskit's default 0 and 1

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  • $\begingroup$ Hello, I think you should try to change the basis at the beginning of your circuit, and check if you have the values you are supposed to get :) $\endgroup$
    – Lena
    Commented Aug 26, 2020 at 8:06
  • $\begingroup$ But how do I change the basis? That is my question. $\endgroup$
    – Tareq Hamarneh
    Commented Aug 26, 2020 at 15:17
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    $\begingroup$ can you add context? What is the Hamiltonian you mention? What basis are you saying is wrong? Please note that questions should be self-contained whenever possible, i.e. not require to read a paper to understand the question $\endgroup$
    – glS ♦
    Commented Aug 26, 2020 at 23:53

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