Ziqi Xu https://helioxv022.github.io/ 2026-09-24T00:00:00Z Ziqi Xu Expressive is not the same as learnable https://helioxv022.github.io/posts/2026-09-structure-matched-learning/ 2026-09-24T00:00:00Z A rotated cluster state is an exact bond-dimension-2 matrix product state, so the complex variational models I trained never lacked the capacity to represent it. How easily each one learned it tracked whether its hidden update had the shape of that two-dimensional memory. What phase disorder does to the GHZ advantage https://helioxv022.github.io/posts/2026-09-ghz-phase-disorder/ 2026-09-23T00:00:00Z With squint, a JAX library for differentiable quantum metrology, the quantum Fisher information of a GHZ sensor array under random signal phases takes a few lines. The Heisenberg advantage disappears, and a handful of X gates brings most of it back. How far do measurement correlations reach in a cluster state? https://helioxv022.github.io/posts/2026-09-cluster-state-cmi/ 2026-09-22T00:00:00Z Measuring a 1D cluster state in a tilted basis correlates distant outcomes. An exact matrix-product-state calculation shows how far those correlations reach.