docs: link to pytket-quest extensions docs

[CalMacCQ]

Description

Adding a crosslink to the extensions index to mention pytket-quest. Should I also mention quest explicitly as a density matrix simulator?

Driveby: mention AerDensityMatrixBackend from pytket-qiskit which was left out until now.

[ferbetanzo]

I'm not sure if we need to mention QuEST in the list of "Density Matrix Simulators" too, given that you use the same QuESTBackend for performing both kinds of simulation and by default it will do state vector simulation.

I can see that the QulacsBackend can also do state vector and density matrix simulations, and by default it also does state vector simulations, however we are listing it as a density matrix simulator in the docs. Do you know why this is?

[CalMacCQ]

I'm not sure if we need to mention QuEST in the list of "Density Matrix Simulators" too, given that you use the same QuESTBackend for performing both kinds of simulation and by default it will do state vector simulation.

I can see that the QulacsBackend can also do state vector and density matrix simulations, and by default it also does state vector simulations, however we are listing it as a density matrix simulator in the docs. Do you know why this is?

I take your point. I guess you have to explicitly enable DM simulation with qulacs. Maybe we should remove the separate mention for qulacs for consistency. Not sure.

I'm happy just mentioning quest as a SV simulator