Memory Separations from a Collective-Spin Quantum Register

Abstract:A spin one-half driven only by total-spin operators generates a renewal process in which one interevent time $n^\ast$ is forbidden while all others occur. No classical hidden Markov model reproduces it with fewer than $1+\sqrt{n^\ast}$ states, an unbounded separation whose only resource is one relative phase of $\pi$. With $K$ amplitudes the same interference yields $K(K{+}1)/2$ decay channels, and for positive weights and generic rates the classical cost is exactly $K(K{+}1)/2$ states. Both are realized by a depth-three circuit whose parameter count does not grow with the register.

arXiv:2610.08038 [quant-ph]

(or arXiv:2610.08038v1 [quant-ph] for this version)

https://doi.org/10.48550/arXiv.2610.08038 Focus to learn more arXiv-issued DOI via DataCite (pending registration)

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