Add `qml.FlipSign` subroutine template

Feature details

It would be great to have a FlipSign operator that supports an integer n or its binary representation, such that:

FlipSign(n)|m> = -|m> if m = n FlipSign(n)|m> = |m> if m != n

That is, to change the sign of a specified state. This would facilitate the process of oracle creation

Implementation

Let guess, we have the binary representation bin_n = [1,0,0,0] and wires = range(4) The template could have the following form:

if bin_n[-1] == 0:
     qml.PauliX(wires = wires[-1])

qml.ctrl(qml.PauliZ, control = wires[:-1], control_values = n[:-1])(wires = wires[-1])

if bin_n[-1] == 0:
     qml.PauliX(wires = wires[-1])

We should check that the dimensions of bin_n and wires are the same. Here I leave a subroutine to pass n to list that can be useful 😃

n = 21
wires = range(5)
bin_string = f"{n:b}".zfill(len(wires))
bin_n = [int(i) for i in bin_string]
print(bin_n)

[1,0,1,0,1]

Steps to take

Implementation

• Create a new subroutine template in the subroutines folder named FlipSign and make it available via qml.FlipSign;
• Allow qml.FlipSign to appear in the relevant parts of the documentation.

See other subroutine templates from the above-linked folder for the details of the implementation and documentation

Testing

Add tests to a new test file to the templates/test_subroutines/ folder. The testing should follow similar to the testing of other subroutines.

How important would you say this feature is?

1: Not important. Would be nice to have.

Additional information

Final example

@qml.qnode(dev)
def circuit():
   qml.Hadamard(wires = 0)
   qml.FlipSign(1, wires = 0)
   qml.Hadamard(wires = 0)
   return qml.sample()

circuit()

[1]

|0> --> |0> + |1> --> |0> - |1> --> |1>

[KetpuntoG]

Yes! Closed 🚀

[sergiomtzlosa]

Hi @KetpuntoG ,

No problem at all!!! I keep working on it.💪

Thanks for the pinpoint path!

[EDIT] Finally here is my file but I think that I have do not understand properly your indications, I think I misunderstood something or I missed something though🤦

Besides this, I still do not understand the test class, can I have some hint about what to do there? Anyway, I am still digging into the code…

Thanks