Using XOR games to benchmark quantum computers

Question

In an answer to a previous question, What exactly are Quantum XOR Games?, ahelwer states:

One application of xor games is self-testing: when running algorithms on an untrusted quantum computer, you can use xor games to verify that the computer isn't corrupted by an adversary trying to steal your secrets!

In an answer to a different previous question, How to benchmark a quantum computer? (which includes a link to Using a simple puzzle game to benchmark quantum computers by James Wootton), DaftWullie suggests blind quantum computation as a general strategy.

How can XOR games be used to perform blind quantum computations to benchmark quantum computers?

Answer 1

If you look at the literature for blind quantum computation, there is the concept of a "trap state". Basically, something that isn't part of the main computation that is supposed to give specific results so that you can easily verify that the computer is behaving as expected. I believe some of these trap states are Bell pairs, and the measurements performed on them are implementing CHSH tests and the like, to verify that there really is (effectively, perhaps hidden by a layer of encoding) a maximally entangled qubit pair present. See, for example, Fig. 2 here.