qiskit/quantum_info/operators/channel/stinespring.py
def _evolve(self, state, qargs=None):
        """Evolve a quantum state by the QuantumChannel.

        Args:
            state (QuantumState): The input statevector or density matrix.
            qargs (list): a list of QuantumState subsystem positions to apply
                           the operator on.

        Returns:
            QuantumState: the output quantum state.

        Raises:
            QiskitError: if the operator dimension does not match the
            specified QuantumState subsystem dimensions.
        """
        # If subsystem evolution we use the SuperOp representation
        if qargs is not None:
            return SuperOp(self)._evolve(state, qargs)

        # Otherwise we compute full evolution directly
        state = self._format_state(state)
        if state.shape[0] != self._input_dim:
            raise QiskitError(
                "QuantumChannel input dimension is not equal to state dimension."
            )
        if state.ndim == 1 and self._data[1] is None and \
           self._data[0].shape[0] // self._output_dim == 1:
            # If the shape of the stinespring operator is equal to the output_dim
            # evolution of a state vector psi -> stine.psi
            return np.dot(self._data[0], state)
        # Otherwise we always return a density matrix
        state = self._format_state(state, density_matrix=True)
        stine_l, stine_r = self._data
        if stine_r is None:
            stine_r = stine_l
        din, dout = self.dim
        dtr = stine_l.shape[0] // dout
        shape = (dout, dtr, din)
        return np.einsum('iAB,BC,jAC->ij', np.reshape(stine_l, shape), state,
                         np.reshape(np.conjugate(stine_r), shape))
def _evolve(self, state, qargs=None):
        """Evolve a quantum state by the QuantumChannel.

        Args:
            state (QuantumState): The input statevector or density matrix.
            qargs (list): a list of QuantumState subsystem positions to apply
                           the operator on.

        Returns:
            QuantumState: the output quantum state.

        Raises:
            QiskitError: if the operator dimension does not match the
            specified QuantumState subsystem dimensions.
        """
        # If subsystem evolution we use the SuperOp representation
        if qargs is not None:
            return SuperOp(self)._evolve(state, qargs)

        # Otherwise we compute full evolution directly
        state = self._format_state(state)
        if state.shape[0] != self._input_dim:
            raise QiskitError(
                "QuantumChannel input dimension is not equal to state dimension."
            )
        if state.ndim == 1 and self._data[1] is None and \
           self._data[0].shape[0] // self._output_dim == 1:
            # If the shape of the stinespring operator is equal to the output_dim
            # evolution of a state vector psi -> stine.psi
            return np.dot(self._data[0], state)
        # Otherwise we always return a density matrix
        state = self._format_state(state, density_matrix=True)
        stine_l, stine_r = self._data
        if stine_r is None:
            stine_r = stine_l
        din, dout = self.dim
        dtr = stine_l.shape[0] // dout
        shape = (dout, dtr, din)
        return np.einsum('iAB,BC,jAC->ij', np.reshape(stine_l, shape), state,
                         np.reshape(np.conjugate(stine_r), shape))
Evolve a quantum state by the QuantumChannel.

        Args:
            state (QuantumState): The input statevector or density matrix.
            qargs (list): a list of QuantumState subsystem positions to apply
                           the operator on.

        Returns:
            QuantumState: the output quantum state.

        Raises:
            QiskitError: if the operator dimension does not match the
            specified QuantumState subsystem dimensions.