Translationally-Invariant Universal Quantum Hamiltonians in 1D
arXiv:2003.13753 · doi:10.1007/s00023-021-01111-7
Abstract
Recent work has characterised rigorously what it means for one quantum system to simulate another, and demonstrated the existence of universal Hamiltonians -- simple spin lattice Hamiltonians that can replicate the entire physics of any other quantum many body system. Previous universality results have required proofs involving complicated `chains' of perturbative `gadgets'. In this paper, we derive a significantly simpler and more powerful method of proving universality of Hamiltonians, directly leveraging the ability to encode quantum computation into ground states. This provides new insight into the origins of universal models, and suggests a deep connection between universality and complexity. We apply this new approach to show that there are universal models even in translationally invariant spin chains in 1D. This gives as a corollary a new Hamiltonian complexity result, that the local Hamiltonian problem for translationally-invariant spin chains in one dimension with an exponentially-small promise gap is PSPACE-complete. Finally, we use these new universal models to construct the first known toy model of 2D--1D holographic duality between local Hamiltonians.
arXiv comment31 pages. V2: extended overview of proof written to make paper clearer. This version of the article has been accepted for publication after peer review, but is not the version of record and does not reflect any post acceptance improvements. The version of record is available online at http://dx.doi.org/10.1007/s00023-021-01111-7
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