Get density matrix

[ikkoham]

Required prerequisites

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Describe the feature

Sometimes we want a density matrix. We can copy the state vector and compute it, but copying becomes a bottleneck, so it would be useful to have a method to compute the density matrix for the vectors on the GPU without copy.

The example of the syntax is

Function

cudaq.get_density_matrix(kernel, qargs=[0, 1, 2])

or
Method for State

state = cudaq.get_state(kernel)
state.get_density_matrix(qargs=[0, 1, 2])