Merge pull request #1359 from qiboteam/hamming_weight

Fix to logic in `quantum_info.hamming_distance`

Author: renatomello

src/qibo/quantum_info/utils.py

@@ -102,9 +102,17 @@ def hamming_distance(
 
     nbits = max(len(bitstring_1), len(bitstring_2))
 
-    difference = abs(int(bitstring_1, 2) - int(bitstring_2, 2))
+    bitstring_1 = "0" * (nbits - len(bitstring_1)) + bitstring_1
+    bitstring_2 = "0" * (nbits - len(bitstring_2)) + bitstring_2
 
-    return hamming_weight(f"{difference:{nbits}b}", return_indexes=return_indexes)
+    difference = np.array(list(bitstring_1), dtype=int) - np.array(
+        list(bitstring_2), dtype=int
+    )
+    difference = np.abs(difference)
+    difference = difference.astype(str)
+    difference = "".join(difference)
+
+    return hamming_weight(difference, return_indexes=return_indexes)
 
 
 def hadamard_transform(array, implementation: str = "fast", backend=None):