supports sparse vector of a quantum state to evaluate expectation value

[ywlds]

for some case we want to evaluate <\psi| H |\psi>.
it seems the mat(H) can get the sparse matrix, while the statevec(\psi) is a dense vector.

How can we make them both sparse to accelerate the numerical calculations?

Many thanks.

[Roger-luo]

If you want to apply gates on the state psi, using a sparse vector won't help much - it will eventually grow to a dense vector anyway.

if you just want to calculate the expectation of a known sparse state, you should directly construct the known state in SparseVector and wrap it in the ArrayReg - the ArrayReg accepts any kind of Julia arrays.