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arXiv:2610.01839

Toward Optimal Circuit Depth for Geometrically Local Hamiltonian Simulation

Zheyu Shen, Yusen Wu, Penghui Yao, Xiao Yuan, Yukun Zhang

quant-phSubmitted Oct 1, 2026• Announced Oct 2, 2026• 0 citations• Revised Oct 2, 2026 (v2)
v1 · Oct 1, 2026v2 · Oct 2, 2026
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Abstract

Understanding the dynamics of interacting quantum systems is a central goal of quantum simulation. For geometrically local Hamiltonians, locality suggests that digital simulation should retain much of the parallelism of the underlying dynamics. For a target accuracy $ε$, we construct a nearest-neighbor quantum circuit that simulates the dynamics of an $n$-qubit, time-independent, finite-range Hamiltonian with normalized local interaction strength on a fixed-dimensional lattice for time $T\ge1$, with circuit depth $O(T\log(nT/ε))$ and gate count $O(nT\log(nT/ε))$. This reduces the polylogarithmic overhead of Haah, Hastings, Kothari, and Low to a single logarithm. On logarithmic-scale blocks from the Lieb--Robinson decomposition, a shallow but highly accurate implementation is essential for reducing the circuit depth. Our key observation is that spatial localization also controls the cost of high precision. In each block, the error of a constant-order product formula is compensated for by a correction, yielding exponential accuracy. The correction can be implemented with depth proportional to the block diameter, introducing no additional asymptotic depth scale beyond that required by spatial localization. Furthermore, we prove an unconditional circuit-depth lower bound for uniform XXZ Hamiltonians: at fixed evolution time $T$ in the stated regime and sufficiently small fixed error $ε$, any nearest-neighbor quantum circuit simulating these dynamics requires depth $Ω(\log n/\log\log n)$. This matches our $O(\log n)$ upper bound up to a doubly logarithmic factor, establishing near-optimal circuit depth for lattice Hamiltonian simulation in this regime. Together, these results clarify the role of locality and precision in determining the circuit complexity of quantum dynamics and suggest broader principles for spatially constrained quantum computation.

Comments
71 pages, 8 figures

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Understanding the dynamics of interacting quantum systems is a central goal of quantum simulation. For geometrically local Hamiltonians, locality suggests that digital simulation should retain much of the parallelism of the underlying dynamics. For a target accuracy εεε, we construct a nearest-neighbor quantum circuit that simulates the dynamics of an nnn-qubit, time-independent, finite-range Hamiltonian with normalized local interaction strength on a fixed-dimensional lattice for time T≥1T\ge1T≥1, with circuit depth O(Tlog⁡(nT/ε))O(T\log(nT/ε))O(Tlog(nT/ε)) and gate count O(nTlog⁡(nT/ε))O(nT\log(nT/ε))O(nTlog(nT/ε)). This reduces the polylogarithmic overhead of Haah, Hastings, Kothari, and Low to a single logarithm. On logarithmic-scale blocks from the Lieb--Robinson decomposition, a shallow but highly accurate implementation is essential for reducing the circuit depth. Our key observation is that spatial localization also controls the cost of high precision. In each block, the error of a constant-order product formula is compensated for by a correction, yielding exponential accuracy. The correction can be implemented with depth proportional to the block diameter, introducing no additional asymptotic depth scale beyond that required by spatial localization.
Furthermore, we prove an unconditional circuit-depth lower bound for uniform XXZ Hamiltonians: at fixed evolution time TTT in the stated regime and sufficiently small fixed error εεε, any nearest-neighbor quantum circuit simulating these dynamics requires depth Ω(log⁡n/log⁡log⁡n)Ω(\log n/\log\log n)Ω(logn/loglogn). This matches our O(log⁡n)O(\log n)O(logn) upper bound up to a doubly logarithmic factor, establishing near-optimal circuit depth for lattice Hamiltonian simulation in this regime. Together, these results clarify the role of locality and precision in determining the circuit complexity of quantum dynamics and suggest broader principles for spatially constrained quantum computation.
Open-system dynamics govern decoherence, transport, and engineered dissipation in quantum many-body systems. We propose a quantum algorithm for simulating time-independent, finite-range Lindblad dynamics with bounded local strength on a constant-dimensional lattice of nnn sites, allowing noncommuting jump operators. For time T≥1T\ge1T≥1 and diamond-norm error at most εεε, it has depth O(Tpolylog⁡(nT/ε))O(T\operatorname{polylog}(nT/ε))O(Tpolylog(nT/ε)) and gate count O(nTpolylog⁡(nT/ε))O(nT\operatorname{polylog}(nT/ε))O(nTpolylog(nT/ε)). These results extend the HHKL spatial decomposition to open systems. The main obstacle is that the reversible overlap corrections used for unitary dynamics have no direct analogue for dissipative channels. We overcome this by retaining the environment in a shared unitary dilation, keeping information lost from the system coherently available and making the spatial corrections reversible. We prove exponential occupation bounds for the environmental states generated by the decomposition, allowing compact representation and coherent simulation of local factors on the inputs that arise. The construction reduces each short-time evolution to a constant number of parallel layers on regions of logarithmic diameter, using nearest-neighbour gates and polylogarithmic auxiliary density. We also prove unconditional worst-case lower bounds using time-independent, purely dissipative processes that transport quantum information. For circuits with local quantum and classical communication, the lower bounds are Ω(nT)Ω(nT)Ω(nT) for the expected gate count and Ω(T)Ω(T)Ω(T) for depth on time scales up to the lattice diameter. They match the upper bounds' leading time and volume dependence up to polylogarithmic factors. At fixed time and sufficiently small fixed error, we further prove a depth lower bound of Ω(log⁡n/log⁡log⁡n)Ω(\log n/\log\log n)Ω(logn/loglogn), showing that global accuracy can require increasing depth as the lattice grows.
We consider the problem of simulating dynamics under geometrically local Lindbladians acting on a lattice of qudits. We present an algorithm to approximate the time evolution under these Lindbladians for evolution time ttt and on NNN qudits to diamond norm error ε\varepsilonε using geometrically local circuits of depth $O(t \ \polylog(Nt/\varepsilon))$. Our results thus achieve a performance comparable to that of the Haah-Hastings-Kothari-Low (HHKL) algorithm for lattice Hamiltonian simulation.
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