qml.shadows.shadow_state¶
-
shadow_state(tape, wires, diffable=False)[source]¶ Transform a circuit returning a classical shadow into one that returns the reconstructed state in a differentiable manner.
- Parameters
tape (QNode or QuantumTape or Callable) – A quantum circuit.
wires (list[int] or list[list[int]]) – If a list of ints, this represents the wires over which to reconstruct the state. If a list of list of ints, a state is reconstructed for every element of the outer list, saving qfunc evaluations.
diffable (bool) – If True, reconstruct the state in a differentiable fashion, where the gradient of the reconstructed state approaches the gradient of the true state in expectation. This comes at a performance cost.
- Returns
The transformed circuit as described in
qml.transform. Executing this circuit will provide the reconstructed state in the form of a tensor.- Return type
qnode (QNode) or quantum function (Callable) or tuple[List[QuantumTape], function]
Example
dev = qml.device("default.qubit", wires=2, shots=10000) @partial(qml.shadows.shadow_state, wires=[0, 1], diffable=True) @qml.qnode(dev) def circuit(x): qml.Hadamard(wires=0) qml.CNOT(wires=[0, 1]) qml.RX(x, wires=0) return qml.classical_shadow(wires=[0, 1])
>>> x = np.array(1.2) >>> circuit(x) array([[ 0.33835 +0.j , -0.01215 +0.2241j , -0.00465 +0.237j , 0.35504997-0.01755j], [-0.01215 -0.2241j , 0.1528 +0.j , 0.16919999-0.0036j , -0.00285 -0.22065j], [-0.00465 -0.237j , 0.16919999+0.0036j , 0.17529999+0.j , 0.0099 -0.2358j ], [ 0.35504997+0.01755j, -0.00285 +0.22065j, 0.0099 +0.2358j , 0.33355 +0.j ]], dtype=complex64) >>> qml.jacobian(lambda x: np.real(circuit(x)))(x) array([[-0.245025, -0.005325, 0.004275, -0.2358 ], [-0.005325, 0.235275, 0.2358 , -0.004275], [ 0.004275, 0.2358 , 0.244875, -0.002175], [-0.2358 , -0.004275, -0.002175, -0.235125]])