Difference in devices


I have a question concerning the difference in the devices provided.

What is the difference between default.qubit and default.mixed in terms of performance. Or what actually makes the two different in terms of functionality.

I am trying to learn a mixed state with the help of qGAN and I understand that it is best to use the default.mixed in such a case, but what do I actually gain from that? I am currently using the cirq.simulator and achieving to learn a mixed state, so I am just curious about what I would gain from changing the simulator.

Additionally, I am wondering how the default.mixed then differs from the PyQuest plugin which is also for working with mixed states. Is it just that this is a high-performance simulator that would lead to a significant speed-up?

Thank you very much.

Hi @sarah_patricia, welcome to the forum!

This is a very good question.

default.qubit is only for pure state simulations. If you want to simulate mixed states then you would have to use default.mixed.

All of the mixed state simulators are built differently so my suggestion would be to try them all out for your particular problem and choose the one that works best for your particular case.

The good thing is that on PennyLane you can simply write your code once and just change the device to try out the different simulators.

Let me know if this helps!