def test_permute_on_state_fn(self):
""" Test if StateFns permute are consistent. """
num_qubits = 4
dim = 2**num_qubits
primitive_list = [1.0 / (i + 1) for i in range(dim)]
primitive_dict = {
format(i, 'b').zfill(num_qubits): 1.0 / (i + 1)
for i in range(dim)
}
dict_fn = DictStateFn(primitive=primitive_dict, is_measurement=True)
vec_fn = VectorStateFn(primitive=primitive_list, is_measurement=True)
# check if dict_fn and vec_fn are equivalent
equivalent = np.allclose(dict_fn.to_matrix(), vec_fn.to_matrix())
self.assertTrue(equivalent)
# permute
indices = [2, 3, 0, 1]
permute_dict = dict_fn.permute(indices)
permute_vect = vec_fn.permute(indices)
equivalent = np.allclose(permute_dict.to_matrix(),
permute_vect.to_matrix())
self.assertTrue(equivalent)
def trace_to_density_op(state: qk.DictStateFn,
trace_over: List[int]) -> qkinfo.DensityMatrix:
"""
Take a state comprised on n qubits and get the trace of the system over the subsystems
specified by a list of indices.
Makes no assumption about the separability of the traced subsystems and gives a density
matrix as a result.
"""
input_statevector = qkinfo.Statevector(state.to_matrix())
return qkinfo.partial_trace(input_statevector, trace_over)
def trace_dict_state(state: qk.DictStateFn,
trace_over: List[int]) -> qk.DictStateFn:
"""
Take a state comprised on n qubits and get the trace of the system over the subsystems
specified by a list of indices.
Assumes state is separable as a DictStateFn can only represent pure states.
"""
input_statevector = qkinfo.Statevector(state.to_matrix())
traced_statevector = qkinfo.partial_trace(input_statevector,
trace_over).to_statevector()
return qk.DictStateFn(traced_statevector.to_dict())