qml.math.dm_from_state_vector

dm_from_state_vector(state, check_state=False, c_dtype='complex128')

Convenience function to compute a (full) density matrix from a state vector.

Parameters

• state (tensor_like) – 1D or 2D tensor state vector. This tensor should of size (2**N,) or (batch_dim, 2**N), for some integer value N.

• check_state (bool) – If True, the function will check the state validity (shape and norm).

• c_dtype (str) – Complex floating point precision type.

Returns

Density matrix of size (2**N, 2**N) or (batch_dim, 2**N, 2**N)

Return type

tensor_like

Example

>>> x = np.array([1, 0, 1j, 0]) / np.sqrt(2)
>>> dm_from_state_vector(x)
array([[0.5+0.j , 0. +0.j , 0. -0.5j, 0. +0.j ],
       [0. +0.j , 0. +0.j , 0. +0.j , 0. +0.j ],
       [0. +0.5j, 0. +0.j , 0.5+0.j , 0. +0.j ],
       [0. +0.j , 0. +0.j , 0. +0.j , 0. +0.j ]])

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