customed (random) unitary operation too hard to define

[Jingze Zhuang]

I want to sample a random unitary circuit. The desired code is like

for _ in 1:10
   @const_gate U = rand(4, 4)
   circuit = chain(2, put((1, 2)=>U)
   psi = zero_state(2)
   apply!(psi, circuit)
end

The problems of redefining the gate U are summarized here:

1. When I repeat this for multiple times, gives too many warnings when redefining U.
2. Such code cannot be put into a function: "World Too New Error"
3. Redefining costs too much time on compilation

[Jinguo Liu (刘金国)]

There is a better way to define a generic block from a matrix. @const is just not designed for it because it creates a new type every time you call it. Please check matblock for generic gates.

julia> for _ in 1:10
          U = matblock(rand(ComplexF64, 4, 4); tag="U")
          circuit = chain(2, put((1, 2)=>U))
          psi = zero_state(2)
          apply!(psi, circuit)
       end

[Jingze Zhuang]

It works well! Thank you so much!