📝 SummarXiv

Abstract

The Learning with Errors (LWE) problem underlies modern lattice-based cryptography and is assumed to be quantum hard. Recent results show that estimating entanglement entropy is as hard as LWE, creating tension with quantum gravity and AdS/CFT, where entropies are computed by extremal surface areas. This suggests a paradoxical route to solving LWE by building holographic duals and measuring extremal surfaces, seemingly an easy task. Three possible resolutions arise: that AdS/CFT duality is intractable, that the quantum-extended Church-Turing thesis (QECTT) fails, or that LWE is easier than believed. We develop and analyze a fourth resolution: that estimating surface areas with the precision required for entropy is itself computationally hard. We construct two holographic quantum algorithms to formalize this. For entropy differences of order N, we show that measuring Ryu-Takayanagi geodesic lengths via heavy-field two-point functions needs exponentially many measurements in N, even when the boundary state is efficiently preparable. For order one corrections, we show that reconstructing the bulk covariance matrix and extracting entropy requires exponential time in N. Although these tasks are computationally intractable, we compare their efficiency with the Block Korkine-Zolotarev lattice reduction algorithm for LWE. Our results reconcile the tension with QECTT, showing that holographic entropy remains consistent with quantum computational limits without requiring an intractable holographic dictionary, and provide new insights into the quantum cryptanalysis of lattice-based cryptography.