fix unitary kraus bug

Author: refraction-ray

CHANGELOG.md

@@ -16,6 +16,10 @@
 
 - Improve the efficiency of `sample_expectation_ps` method by using cached state.
 
+### Fixed
+
+- Fixed `unitary_kraus` of Circuit class support for multi-qubit kraus channels, previous implementation fails to reshape the kraus tensor as matrix
+
 ## 0.5.0
 
 ### Added

tensorcircuit/circuit.py

@@ -393,6 +393,7 @@ def _unitary_kraus_template(
         sites = len(index)
         kraus = [k.tensor if isinstance(k, tn.Node) else k for k in kraus]
         kraus = [gates.array_to_tensor(k) for k in kraus]
+        kraus = [backend.reshapem(k) for k in kraus]
         if prob is None:
             prob = [
                 backend.real(backend.trace(backend.adjoint(k) @ k) / k.shape[0])