Improve noisy tomography bases

qiskit_experiments/library/tomography/basis/base_basis.py

@@ -100,7 +100,14 @@ class PreparationBasis(BaseBasis):
 
     @abstractmethod
     def matrix_shape(self, qubits: Sequence[int]) -> Tuple[int, ...]:
-        """Return the shape of subsystem dimensions of a matrix element."""
+        """Return the shape of subsystem dimensions of the state :py:attr:`~matrix`.
+
+        Args:
+            qubits: the physical qubit subsystems.
+
+        Returns:
+            A tuple of subsystem dimensions for the specified qubits.
+        """
 
     @abstractmethod
     def matrix(self, index: Sequence[int], qubits: Optional[Sequence[int]] = None) -> np.ndarray:
@@ -152,11 +159,25 @@ class MeasurementBasis(BaseBasis):
 
     @abstractmethod
     def outcome_shape(self, qubits: Sequence[int]) -> Tuple[int, ...]:
-        """Return the shape of allowed measurement outcomes on specified qubits."""
+        """Return the shape of allowed measurement outcomes on specified qubits.
+
+        Args:
+            qubits: the physical qubit subsystems.
+
+        Returns:
+            A tuple of the number of measurement outcomes for specified qubits.
+        """
 
     @abstractmethod
     def matrix_shape(self, qubits: Sequence[int]) -> Tuple[int, ...]:
-        """Return the shape of subsystem dimensions of a POVM matrix element."""
+        """Return the shape of subsystem dimensions of a POVM :py:attr:`~matrix`.
+
+        Args:
+            qubits: the physical qubit subsystems.
+
+        Returns:
+            A tuple of subsystem dimensions for the specified qubits.
+        """
 
     @abstractmethod
     def matrix(

qiskit_experiments/library/tomography/basis/cache_method.py

@@ -0,0 +1,68 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2022.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+"""
+Method decorator for caching regular methods in class instances.
+"""
+
+from typing import Dict, Callable, Optional
+import functools
+
+
+def _method_cache_name(instance: any) -> str:
+    """Attribute name for storing cache in an instance"""
+    return "_CACHE_" + type(instance).__name__
+
+
+def _get_method_cache(instance: any) -> Dict:
+    """Return instance cache for cached methods"""
+    cache_name = _method_cache_name(instance)
+    try:
+        return getattr(instance, cache_name)
+    except AttributeError:
+        setattr(instance, cache_name, {})
+        return getattr(instance, cache_name)
+
+
+def cache_method(maxsize: Optional[int] = None) -> Callable:
+    """Decorator for caching class instance methods.
+
+    Args:
+        maxsize: The maximum size of this method's LRU cache.
+
+    Returns:
+        The decorator for caching methods.
+    """
+
+    def cache_method_decorator(method: Callable) -> Callable:
+        """Decorator for caching method.
+
+        Args:
+            method: A method to cache.
+
+        Returns:
+            The wrapped cached method.
+        """
+
+        @functools.wraps(method)
+        def _cached_method(self, *args, **kwargs):
+            cache = _get_method_cache(self)
+            key = method.__name__
+            try:
+                meth = cache[key]
+            except KeyError:
+                meth = cache[key] = functools.lru_cache(maxsize)(functools.partial(method, self))
+
+            return meth(*args, **kwargs)
+
+        return _cached_method
+
+    return cache_method_decorator