Add Fourier interferometers explicitly to Perceval

[anthonyrtw]

Fourier interferometers are possibly the most commonly used optical component/circuit that is not directly available in Perceval currently.

Here, I've defined a Fourier interferometer class UFT(Unitary) that can be immediately defined:

from perceval import *
fourier_circuit = Circuit(m) // UFT(m)

This saves the user from calculating the Matrix form of Fourier interferometers and then explicitly defining the matrix as a Unitary.

I have also made it available from root.

[anthonyrtw]

I have renamed the class to FourierUnitary to maintain connection with its parent class Unitary. But have left the default name as "UFT" for display purposes.

(I have also set the rendering so that it renders in lightblue. This should work with Latex/HTML.)

[Aubaert]

I have renamed the class to FourierUnitary to maintain connection with its parent class Unitary. But have left the default name as "UFT" for display purposes.

(I have also set the rendering so that it renders in lightblue. This should work with Latex/HTML.)

I find it weird that the default displayed name is not the name of the class, and not even the first letter of each word.
Also, the lightblue color is already the color of a sub-circuit when using a recursive display. It would be better to find an unused color (you can use pink if you want to keep a light tone color)

[anthonyrtw]

The colour is now "thistle" & the name is identical to the class name:

[Aubaert]

I added the serialization for the new component (so it won't be serialized as a regular Unitary). This will require a new version of exqalibur to work with the CircuitOptimizer. Also, this will require updating perceval on the cloud side so it can understand what we are using

[Aubaert]

As you said this class was used in some notebooks, can you update them so they use this new method ?

[Aubaert]

Update the doc (it's not random)