This is a non-exhaustive, but growing list of common pitfalls when using jaxquantum.

JAX

Quote

When walking about the countryside of Italy, the people will not hesitate to tell you that JAX has “una anima di pura programmazione funzionale”. ~ JAX docs

Often the sharp bits poking at you originate from the functional paradigm within which JAX operates. The JAX developers have compiled a great list of these common "gotchas": https://docs.jax.dev/en/latest/notebooks/Common_Gotchas_in_JAX.html

Operations

Tensor product shorthand ^

Note that the shorthand for tensor product ^ is evaluated after other basic math operations (e.g. +,-,*,/,@). So, when using this shorthand, it is best practice to use parentheses.

Tensor shorthand.

For example, the following code will fail:

jqt.identity(2)^jqt.identity(3) + jqt.identity(2)^jqt.identity(3)

Output

ValueError: Dimensions are incompatible: ((3,), (3,)) and ((2,), (2,))

This is because jqt.identity(3) + jqt.identity(2) is running before the tensor products.

Instead, we should use parentheses to specify the order of operations to begin with ^.

(jqt.identity(2)^jqt.identity(3)) + (jqt.identity(2)^jqt.identity(3))

Output

Quantum array: dims = ((2, 3), (2, 3)), bdims = (), shape = (6, 6), type = oper
Qarray data =
[[2.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j]
[0.+0.j 2.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j]
[0.+0.j 0.+0.j 2.+0.j 0.+0.j 0.+0.j 0.+0.j]
[0.+0.j 0.+0.j 0.+0.j 2.+0.j 0.+0.j 0.+0.j]
[0.+0.j 0.+0.j 0.+0.j 0.+0.j 2.+0.j 0.+0.j]
[0.+0.j 0.+0.j 0.+0.j 0.+0.j 0.+0.j 2.+0.j]]