Sign-curing local Hamiltonians: termwise versus global stoquasticity and the use of Clifford transformations

07/23/2020

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by   Marios Ioannou, et al.

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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 Σ_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.