Circuit lower bounds for low-energy states of quantum code Hamiltonians

Abstract

The No Low-energy Trivial States (NLTS) conjecture of Freedman and Hastings, 2014 -- which posits the existence of a local Hamiltonian with a super-constant quantum circuit lower bound on the complexity of all low-energy states -- identifies a fundamental obstacle to the resolution of the quantum PCP conjecture. In this work, we provide new techniques, based on entropic and local indistinguishability arguments, that prove circuit lower bounds for all the low-energy states of local Hamiltonians arising from quantum error-correcting codes. For local Hamiltonians arising from nearly linear-rate or nearly linear-distance LDPC stabilizer codes, we prove super-constant circuit lower bounds for the complexity of all states of energy o(n). Such codes are known to exist and are not necessarily locally testable, a property previously suspected to be essential for the NLTS conjecture. Curiously, such codes can also be constructed on a two-dimensional lattice, showing that low-depth states cannot accurately approximate the ground-energy even in physically relevant systems.

Previous versions contain revisions to introduction and non-technical content. Prior to version 3, asymptotic constants were worse and the dependency in Theorem 1 was epsilon^{1/3}. Version 5 introduced the lower bound for linear-distance LDPC stabilizer codes which was not in previous versions as well as additional technical appendices

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Cited by in corpus (5)

• NLTS Hamiltonians from good quantum codes
• Symmetry-enforced many-body separability transitions
• Exponential clustering of bipartite quantum entanglement at arbitrary temperatures
• Concentration bounds for quantum states and limitations on the QAOA from polynomial approximations
• Combinatorial NLTS From the Overlap Gap Property