qml.qinfo.transforms.vn_entropy¶
- vn_entropy(tape, wires, base=None, **kwargs)[source]¶
Compute the Von Neumann entropy from a
QuantumTapereturning astate().\[S( \rho ) = -\text{Tr}( \rho \log ( \rho ))\]Warning
The
qml.qinfo.vn_entropytransform is deprecated and will be removed in v0.40. Instead, include thepennylane.vn_entropy()measurement process in the return line of your QNode.- Parameters
tape (QNode or QuantumTape or Callable) – A quantum circuit returning a
state().wires (Sequence(int)) – List of wires in the considered subsystem.
base (float) – Base for the logarithm, default is None the natural logarithm is used in this case.
- Returns
The transformed circuit as described in
qml.transform. Executing this circuit will provide the Von Neumann entropy in the form of a tensor.- Return type
qnode (QNode) or quantum function (Callable) or tuple[List[QuantumTape], function]
Example
It is possible to obtain the entropy of a subsystem from a
QNodereturning astate().dev = qml.device("default.qubit", wires=2) @qml.qnode(dev) def circuit(x): qml.IsingXX(x, wires=[0, 1]) return qml.state()
>>> vn_entropy(circuit, wires=[0])(np.pi/2) 0.6931471805599453
The function is differentiable with backpropagation for all interfaces, e.g.:
>>> param = np.array(np.pi/4, requires_grad=True) >>> qml.grad(vn_entropy(circuit, wires=[0]))(param) tensor(0.62322524, requires_grad=True)
See also