Field-aligned measurement removes the anisotropy barrier of sample-based quantum subspace solvers for magnetized-plasma heat conduction

arXiv:2611.07102v1 Announce Type: new Abstract: Sample-based quantum subspace methods construct a small subspace from measured basis states and solve the target problem classically within it. We study these methods for heat conduction in magnetized plasmas, where the anisotropy $\chi_\parallel/\chi_\perp$ reaches $10^8$ to $10^{10}$. We prove two results for the energy-norm Galerkin solution. First, if the measurement basis is aligned with the flux surfaces and the subspace contains the poloidal-mode-zero block, the error is bounded by $\|r_0\|_{L^+}(\chi_\parallel-\chi_\perp)^{-1/2}$, where the numerator does not depend on $\chi_\parallel$. The bound is sharp, so the accuracy improves as the anisotropy grows.