A 1-bit quantum filter for particle trajectory reconstruction

Abstract

Cite this article as: Chiotopoulos, X., Nicotra, D., Scriven, G. et al. A 1-bit quantum filter for particle trajectory reconstruction. Commun Phys (2026). ABSTRACT 13 The transition to the High-Luminosity Large Hadron Collider (HL-LHC) presents a computational challenge where particle reconstruction complexity may outpace classical computing resources. While quantum computing offers potential speedups, standard algorithms like Harrow-Hassidim-Lloyd (HHL) require prohibitive circuit depths for near-term hardware. Here, we introduce a 1-Bit Quantum Filter, a domain-specific adaptation of HHL that reformulates tracking from matrix inversion to binary ground-state filtering. By replacing high-precision phase estimation with a single-ancilla spectral threshold and exploiting the Hamiltonian's sparsity, we achieve an asymptotic gate complexity of O(√ N log N), given Hamiltonian dimension N. We validate this approach on LHCb Monte Carlo events, demonstrating segment finding efficiency highly competitive with the classical state-of-the-art methods. Furthermore, we benchmark performance using the Quantinuum System Model H2 trapped-ion processor and IBM Heron R3 superconducting processor. This work establishes a quantum track reconstruction method capable of solving realistic event topologies on noise-free simulators and smaller tracking scenarios within the current constraints of the Noisy Intermediate Scale Quantum (NISQ) era. Remaining challenges toward a full end-to-end tracking solution include an efficient readout and Hamiltonian construction. 14