Remove LegacyFermionicOp (#314)

* Remove LegacyFermionicOp * improve performance by change internal data structure * compose preserves the label type * rename to display_format and add to_list(display_format) Co-authored-by: Max Rossmannek <[email protected]> Co-authored-by: Steve Wood <[email protected]> Co-authored-by: Max Rossmannek <[email protected]>
qiskit-community · Aug 17, 2021 · 1d973e5 · 1d973e5
1 parent 9c130b7
commit 1d973e5
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diff --git a/qiskit_nature/mappers/second_quantization/qubit_mapper.py b/qiskit_nature/mappers/second_quantization/qubit_mapper.py
@@ -16,12 +16,12 @@
 from typing import List, Tuple
 
 import numpy as np
-
 from qiskit.opflow import PauliSumOp
 from qiskit.quantum_info.operators import Pauli, SparsePauliOp
 
 from qiskit_nature import QiskitNatureError
 from qiskit_nature.operators.second_quantization import SecondQuantizedOp
+from qiskit_nature.operators.second_quantization.fermionic_op import FermionicOp
 
 
 class QubitMapper(ABC):
@@ -107,7 +107,12 @@ def times_annihilation_op(position, pauli_table):
 
         # TODO to_list() is not an attribute of SecondQuantizedOp. Change the former to have this or
         #   change the signature above to take FermionicOp?
-        for label, coeff in second_q_op.to_list():
+        label_coeff_list = (
+            second_q_op.to_list(display_format="dense")
+            if isinstance(second_q_op, FermionicOp)
+            else second_q_op.to_list()
+        )
+        for label, coeff in label_coeff_list:
 
             ret_op = SparsePauliOp(Pauli((all_false, all_false)), coeffs=[coeff])