Sign-curing local Hamiltonians: termwise versus global stoquasticity and the use of Clifford transformations.
Marios Ioannou, Stephen Piddock, Milad Marvian, Joel Klassen, Barbara M. Terhal · arXiv (Cornell University) · 2020
We elucidate the distinction between global and termwise stoquasticity for local Hamiltonians and prove several complexity results. We prove coNP-hardness of deciding global stoquasticity in a fixed basis and $\Sigma_2^p$-hardness of deciding global stoquasticity under single-qubit transformations. We expand the class of sign-curing transformations by showing how Clifford transformations can sign-cure a class of disordered 1D XYZ Hamiltonians.