AmplitudeEmbedding acts on the entire system (all wires) by calling the
QubitStateVector function. This prepares the given state by using the required gates.
If you use a PennyLane plugin that supports a quantum simulator device like PennyLane’s
default.qubit or Qiskit, this function simulates your state. If you use a PennyLane plugin that supports a quantum hardware device like Forest SDK, it should correspond to initialising this state in the hardware.
The documention says that it doesn’t work on all device, I could not find on which devices it works.
This refers to the fact that
QubitStateVector (and hence
AmplitudeEmbedding) is a qubit state preparation function. Hence, it will only work with devices that simulate discrete variable computing. It will not work if you use
default.gaussian device, for example. You can use this with
default.qubit, Rigetti Forest SDK, Qiskit plugins.