Can anyone please point me to the current state of the art way to do Quantum Computing in Mathematica?
As Mathematica has most necessary matrix algebra functions (crucially the matrix exponential) built in natively (both for symbolic and numerics) it is quite simple to roll most things yourself. For more complicated manipulations QuantumUtils is useful (disclaimer this was made by some colleagues).
I should point out that the focus of this library is not on building and simulating algorithms (although possible) but the description and manipulation of quantum channels and hamiltonians. Hamiltonian simulation and GRAPE pulse design is also baked in.
Completely out of my domain of expertise, however I stumbled across the "Live CEOing" videos Wolfram is doing on YouTube. Quantum computing seems to be a focus. For example:
Looks to be destined for the Wolfram Language and Mathematica in the future. Not sure if it is of interest to you, but thought I would mention it. Clearly not something available now though.