feat: sketched the general structure of a qml model

src/qiboml/models/abstract.py

@@ -0,0 +1,64 @@
+"""Defines the general structure of a qiboml module"""
+
+from abc import ABC, abstractmethod
+from dataclasses import dataclass
+
+from qibo import Circuit
+
+from qiboml.backends import JaxBackend
+
+
+@dataclass
+class QuantumCircuitLayer(ABC):
+
+    circuit: Circuit = None
+    backend: "qibo.backends.Backend" = JaxBackend()
+
+    @abstractmethod
+    def __post_init__(self):
+        pass
+
+    @abstractmethod
+    def _feed_input(self, x):
+        pass
+
+    def forward(self, x):
+        """Performs the forward pass: prepares the input and execute the circuit."""
+        self._feed_input(x)
+        return self.backend.execute_circuit(self.circuit)
+
+    @abstractmethod
+    def backward(self, input_grad: "ndarray"):
+        pass
+
+    @property
+    def parameters(self):
+        return self.circuit.get_parameters()
+
+    @parameters.setter
+    def parameters(self, x: "ndarray"):
+        self.circuit.set_parameters(x)
+
+
+@dataclass
+class SequentialQuantumModel(QuantumCircuitLayer):
+
+    layers: list[QuantumCircuitLayer] = []
+
+    def __post_init__(self):
+        # in principle differently sized circuits might be passed
+        nqubits = max([layer.circuit.nqubits for layer in self.layers])
+        self.circuit = Circuit(nqubits)
+        for layer in self.layers:
+            circ = Circuit(nqubits)
+            circ.add(layer.circuit.on_qubits(*range(layer.circuit.nqubits)))
+            self.circuit = self.circuit + circ
+
+    def _feed_input(self, x):
+        self.layers[0]._feed_input(x)
+
+    def backward(self, input_grad: "ndarray"):
+        grad = input_grad
+        for layer in self.layers:
+            grad = layer.backward(grad)
+        return grad

src/qiboml/models/encoding_decoding.py

@@ -0,0 +1,35 @@
+"""Some standard encoding and decoding layers"""
+
+from qiboml.models.abstract import QuantumCircuitLayer
+
+
+class QuantumEncodingLayer(QuantumCircuitLayer):
+    pass
+
+
+class PhaseEncodingLayer(QuantumEncodingLayer):
+    pass
+
+
+class AmplitudeEncodingLayer(QuantumEncodingLayer):
+    pass
+
+
+"""
+   .
+   .
+   .
+   .
+"""
+
+
+class QuantumDecodingLayer(QuantumCircuitLayer):
+    pass
+
+
+"""
+   .
+   .
+   .
+   .
+"""