Hi there!
Lately I’ve been playing with the Stepper backend and I have couple of question on the topic:

In the method apply(), I’m not sure what should I enter as
r : List[int]
parameter.
As far as I understood, the logic is the following: provided aStateVector
on the modesm_1, ..., m_n
, I apply the the circuitc: ACircuit
only on the portion that goes fromr[0] = m_i
tor[1] = m_j
.
Is it correct? 
Since the state is sliced and then reconverted to in a
BasicState
(here), I’d say that this backend now ignores the annotations right? 
At the moment I am working with completely mixed states and I create my state using the
SVDistribution
class. At the moment I’m manually unpacking the dictionary and feeding to the backend. Would it be hard to extend the stepper also for these states?
I also have a couple of curiosities:

when the detector class, along with some interesting features like dark noise, will be ready?

would it be demanding to add to the platform some components that model noisy channels (i.e. bit flip, phase flip, bitphase and depolarization)? It would be of great help in my work.
Thanks for your attention
Francesco
P.s. The _compute_unitary
method of the Beam splitter has been modified in latest release right? cos_theta = sqrt(R)
is inconsistent with the documentation.