feat: integrating qmatchatea SimulationResult in the circuit execution

.pre-commit-config.yaml

@@ -19,7 +19,7 @@ repos:
       - id: isort
         args: ["--profile", "black"]
   - repo: https://github.com/PyCQA/docformatter
-    rev: master
+    rev: v1.7.5
     hooks:
       - id: docformatter
         additional_dependencies: [tomli]

src/qibotn/backends/qmatchatea.py

@@ -1,35 +1,57 @@
-"""Implementation of Quantum Matcha Tea backend"""
+"""Implementation of Quantum Matcha Tea backend."""
 
 from dataclasses import dataclass
+
+from qibo.config import raise_error
 from qiskit import QuantumCircuit
 
 from qibotn.backends.abstract import QibotnBackend
-from qibo.config import raise_error
+
 
 @dataclass
 class QMatchaTeaBackend(QibotnBackend):
 
     def __init__(self):
         super().__init__()
+        import qiskit  # pylint: disable=import-error
         import qmatchatea  # pylint: disable=import-error
-        import qiskit   # pylint: disable=import-error
+        import qtealeaves  # pylint: disable=import-error
-        import qtealeaves    # pylint: disable=import-error
 
         self.qmatchatea = qmatchatea
         self.qiskit = qiskit
         self.qtleaves = qtealeaves
 
-
         # Set default configurations
         self.configure_tn_simulation()
         # TODO: update this function whenever ``set_device`` and ``set_precision``
         # are set (?)
         self._setup_qmatchatea_backend()
+        self._observables = self.qtleaves.observables.TNObservables()
 
+    @property
+    def observables(self):
+        """Observables measured after TN execution."""
+        return self._observables
+
+    @observables.setter
+    def observables(self, observables: list):
+        """Set the observables to be measured after TN execution.
+
+        It accepts a list
+        of objects among the ones proposed in ``qtealeaves.observables``.
+        """
+        for obs in observables:
+            if isinstance(obs, self.qtleaves.observables.tnobase._TNObsBase):
+                self._observables = self.qtleaves.observables.TNObservables()
+                self._observables += obs
+            else:
+                raise TypeError("Expected an instance of TNObservables")
 
     def execute_circuit(
-            self, circuit, initial_state=None, nshots=None, return_array=False
+        self, circuit, initial_state=None, nshots=None, return_array=False
     ):
+        """Preserve the Qibo execution interface, but return Quantum Matcha Tea
+        ``SimulationResult`` object."""
 
         # TODO: verify if the QCIO mechanism of matcha is supported by Fortran only
         # as written in the docstrings or by Python too (see ``io_info`` argument of
@@ -37,36 +59,32 @@ class QMatchaTeaBackend(QibotnBackend):
         if initial_state is not None:
             raise_error(
                 NotImplementedError,
-                f"Backend {self.name}-{self.platform} currently does not support initial state."
+                f"Backend {self.name}-{self.platform} currently does not support initial state.",
             )
 
         # TODO: do we want to keep it like this or we aim to implement a different
         # idea of "shots" here?
-        nshots = None
-        
         circuit = self._qibocirc_to_qiskitcirc(circuit)
 
         run_qk_params = self.qmatchatea.preprocessing.qk_transpilation_params(False)
 
         results = self.qmatchatea.run_simulation(
-            circ = circuit,
+            circ=circuit,
-            convergence_parameters = self.convergence_params,
+            convergence_parameters=self.convergence_params,
-            transpilation_parameters = run_qk_params,
+            transpilation_parameters=run_qk_params,
-            backend = self.qmatchatea_backend,
+            backend=self.qmatchatea_backend,
+            observables=self._observables,
         )
 
-        # TODO: construct a proper TNResult object?
+        # TODO: construct a proper TNResult in Qibo?
-        # It does not make sense to reconstruct QuantumState here!
+        return results
-        return results.measure_probabilities
-
 
     def configure_tn_simulation(
-            self, 
+        self,
-            convergence_params = None,
+        convergence_params=None,
-            ansatz: str = "MPS",
+        ansatz: str = "MPS",
-        ):
+    ):
-        """
+        """Configure TN simulation given Quantum Matcha Tea interface.
-        Configure TN simulation given Quantum Matcha Tea interface.
 
         Args:
             ansatz (str): tensor network ansatz. It can be  tree tensor network "TTN"
@@ -79,25 +97,29 @@ class QMatchaTeaBackend(QibotnBackend):
         """
 
         # Set configurationsor defaults
-        self.convergence_params = convergence_params or self.qmatchatea.QCConvergenceParameters()
+        self.convergence_params = (
+            convergence_params or self.qmatchatea.QCConvergenceParameters()
+        )
         self.ansatz = ansatz
 
-        # Initializing the TNObservables according to qmatchatea 
-        self.observables = self.qtleaves.observables.TNObservables()
-
-
     def _setup_qmatchatea_backend(self):
         """Configure qmatchatea QCBackend object."""
 
-        self.qmatchatea_device = "cpu" if "CPU" in self.device else "gpu" if "GPU" in self.device else None
+        self.qmatchatea_device = (
-        self.qmatchatea_precision = "C" if self.precision == "single" else "Z" if self.precision == "double" else "A"
+            "cpu" if "CPU" in self.device else "gpu" if "GPU" in self.device else None
+        )
+        self.qmatchatea_precision = (
+            "C"
+            if self.precision == "single"
+            else "Z" if self.precision == "double" else "A"
+        )
 
         # TODO: once MPI is available for Python, integrate it here
         self.qmatchatea_backend = self.qmatchatea.QCBackend(
-            backend = "PY",  # The only alternative is Fortran, but we use Python here
+            backend="PY",  # The only alternative is Fortran, but we use Python here
-            precision = self.qmatchatea_precision,
+            precision=self.qmatchatea_precision,
-            device = self.qmatchatea_device,
+            device=self.qmatchatea_device,
-            ansatz = self.ansatz,
+            ansatz=self.ansatz,
         )
 
     def _qibocirc_to_qiskitcirc(self, qibo_circuit) -> QuantumCircuit:
@@ -110,7 +132,6 @@ class QMatchaTeaBackend(QibotnBackend):
         # with the constraint of having only the gates basis_gates
         qiskit_circuit = self.qmatchatea.preprocessing.preprocess(
             qiskit_circuit,
-            qk_params=self.qmatchatea.preprocessing.qk_transpilation_params()
+            qk_params=self.qmatchatea.preprocessing.qk_transpilation_params(),
         )
-
         return qiskit_circuit