← 研踪 PaperTrailarXiv:2610.02166 · v2
Beyond light cones: State preparation complexity in quantum spin glasses
首次提交 2026-10-02 01:55
版本更新 2026-11-03 00:41
雷达观测 2026-11-04 23:41
摘要
We introduce a technique for studying state preparation complexity in the quantum $p$-spin model on $n$ qubits, a disordered quantum spin system with random interactions on every set of $p$ qubits. We reduce the task of proving state preparation lower bounds to bounding the local profile complexity of the class, a quantity derived from the metric entropy of the set of vectors recording each state's expectation values against all weight-$p$ Pauli strings. We show that, for sufficiently large fixed $p$, any class with local profile complexity $O(n^2)$ remains separated from the ground-state energy by $Ω(\sqrt n)$, a gap on the leading energy scale. When the profile complexity is $o(n^2)$, we prove the stronger conclusion that the class cannot outperform a benchmark class of simpler states at leading order. Product states always provide such a benchmark. Our framework strengthens known bounds and covers classes beyond the reach of previous methods. These include examples where circuit lightcones extend across the entire system, preventing an application of standard arguments. We obtain an $Ω(n^2/\log n)$ gate lower bound for preparing near-ground states and depth--width tradeoffs, allowing arbitrary one- and two-qubit gates and arbitrarily many discardable ancillas. We also derive lower bounds on entanglement depth and matrix product state bond dimension, and energy obstructions for forward and reverse magic at every fixed level of Parham's magic hierarchy (arXiv:2504.19966). For Clifford circuits doped with $T$-gates, we obtain sharper energy comparisons using product stabilizer states as a more restrictive benchmark. The proof combines an adaptation of a nonsymmetric quantum de Finetti theorem (arXiv:1810.12197) with metric-entropy bounds for the Gaussian process indexed by the local profiles of states in the class.
作者备注：102 pages
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v2 · 2026-11-03 00:41 · 最新观测版本
Beyond light cones: State preparation complexity in quantum spin glasses
We introduce a technique for studying state preparation complexity in the quantum $p$-spin model on $n$ qubits, a disordered quantum spin system with random interactions on every set of $p$ qubits. We reduce the task of proving state preparation lower bounds to bounding the local profile complexity of the class, a quantity derived from the metric entropy of the set of vectors recording each state's expectation values against all weight-$p$ Pauli strings. We show that, for sufficiently large fixed $p$, any class with local profile complexity $O(n^2)$ remains separated from the ground-state energy by $Ω(\sqrt n)$, a gap on the leading energy scale. When the profile complexity is $o(n^2)$, we prove the stronger conclusion that the class cannot outperform a benchmark class of simpler states at leading order. Product states always provide such a benchmark. Our framework strengthens known bounds and covers classes beyond the reach of previous methods. These include examples where circuit lightcones extend across the entire system, preventing an application of standard arguments. We obtain an $Ω(n^2/\log n)$ gate lower bound for preparing near-ground states and depth--width tradeoffs, allowing arbitrary one- and two-qubit gates and arbitrarily many discardable ancillas. We also derive lower bounds on entanglement depth and matrix product state bond dimension, and energy obstructions for forward and reverse magic at every fixed level of Parham's magic hierarchy (arXiv:2504.19966). For Clifford circuits doped with $T$-gates, we obtain sharper energy comparisons using product stabilizer states as a more restrictive benchmark. The proof combines an adaptation of a nonsymmetric quantum de Finetti theorem (arXiv:1810.12197) with metric-entropy bounds for the Gaussian process indexed by the local profiles of states in the class.
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