one hot encoding

[skushnir123]

Simple bloq to implement a one-hot encoding. This will be used in a subroutine of QROM Inverse (PR forthcoming)

[fdmalone]

Some small nits and suggestions. Looking good!

[tanujkhattar]

You can use cirq.CSWAP here and the it'll automatically ge tconverted to TwoBitCSwap whenever the bloq-api is used due to the _cirq_gate_to_bloq logic.

[tanujkhattar]

In fact, let's change the decomposition and build_call_graph to delegate to SwapWithZero bloq

[tanujkhattar]

Isn't this same as the SwapWithZero gate we already have?

[tanujkhattar]

You can essentially write a one hot encoding bloq by doing an X(q[0]) and then call SwapWithZero with a as control and b as target.
The part after the first X gate is SwapWithZero bloq.

Also, SwapWithZero now supports N-dimensional registers so you can also do a one-hot for a multi dimensional input / output register. For example, if you have a 3d data where the input is 3 selection registers (a_x, a_y, a_z) and target is a 3D encoding where you would set target[x][y][z] = 1 when a_x = x, a_y = y and a_z = z; you can do this again by setting target[0][0][0] = 1 and calling a 3D swap-with-zero.

[fdmalone]

There's no issue with swap with zero destroying the rest of the "b" register here? I've always been confused by when SwapWithZero is ok to use.

[tanujkhattar]

The |B> register is assumed to be |0> in this case, so it doesn't matter how you permute it it will continue to be 0 everywhere except the x'th bit where you'll have a 1 since you swapped 0 <-> x .

The circuit after the first X gate is the same circuit as used for SwapWithZero

[fdmalone]

cool

[tanujkhattar]

I'll mark this as request changes following my comments above.