arXiv subjects

Marcel Merk

Publications and source records attributed to Marcel Merk.

7 recordsLinked to original sources

arXiv2026

A 1-bit quantum filter for particle trajectory reconstruction

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 the 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 $O(\sqrt{N} \log N)$, given Hamiltonian dimension $N$. We validate this approach by simulating LHCb Vertex Locator events with a toy model, and benchmark performance using the noise models of Quantinuum H2 trapped-ion and IBM Heron superconducting processors. This work establishes a resource-efficient 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.

quant-ph↗

arXiv2025

Variational Quantum Algorithms for Particle Track Reconstruction

Quantum Computing is a rapidly developing field with the potential to tackle the increasing computational challenges faced in high-energy physics. In this work, we explore the potential and limitations of variational quantum algorithms in solving the particle track reconstruction problem. We present an analysis of two distinct formulations for identifying straight-line tracks in a multilayer detection system, inspired by the LHCb vertex detector. The first approach is formulated as a ground-state energy problem, while the second approach is formulated as a system of linear equations. This work addresses one of the main challenges when dealing with variational quantum algorithms on general problems, namely designing an expressive and efficient quantum ansatz working on tracking events with fixed detector geometry. For this purpose, we employed a quantum architecture search method based on Monte Carlo Tree Search to design the quantum circuits for different problem sizes. We provide experimental results to test our approach on both formulations for different problem sizes in terms of performance and computational cost.

quant-ph↗

arXiv2025

TrackHHL: A Quantum Computing Algorithm for Track Reconstruction at the LHCb

In the future high-luminosity LHC era, high-energy physics experiments face unprecedented computational challenges for event reconstruction. Employing the LHCb vertex locator as a case study we investigate a novel approach for charged particle track reconstruction. The algorithm hinges on minimizing an Ising-like Hamiltonian using matrix inversion. Solving this matrix inversion classically achieves reconstruction efficiencies akin to current state-of-the-art algorithms. Exploiting the Harrow-Hassidim-Lloyd (HHL) quantum algorithm for linear systems holds the promise of an exponential speedup in the number of input hits over its classical counterpart, contingent on the conditions of efficient quantum phase estimation (QPE) and effectively reading out the algorithm's output. This contribution builds on previous work by Nicotra et al and strives to fulfill these conditions and further streamlines the algorithm's circuit depth by a factor up to $10^4$. Our version of the HHL algorithm restricts the QPE precision to one bit, largely reducing circuit depth and addressing HHL's readout issue. Furthermore, this allows for the implementation of a post-processing algorithm that reconstructs event Primary Vertices (PVs). The findings presented here aim to further illuminate the potential of harnessing quantum computing for the future of particle track reconstruction in high-energy physics.

quant-ph↗

arXiv2023

A quantum algorithm for track reconstruction in the LHCb vertex detector

High-energy physics is facing increasingly computational challenges in real-time event reconstruction for the near-future high-luminosity era. Using the LHCb vertex detector as a use-case, we explore a new algorithm for particle track reconstruction based on the minimisation of an Ising-like Hamiltonian with a linear algebra approach. The use of a classical matrix inversion technique results in tracking performance similar to the current state-of-the-art but with worse scaling complexity in time. To solve this problem, we also present an implementation as quantum algorithm, using the Harrow-Hassadim-Lloyd (HHL) algorithm: this approach can potentially provide an exponential speedup as a function of the number of input hits over its classical counterpart, in spite of limitations due to the well-known HHL Hamiltonian simulation and readout problems. The findings presented in this paper shed light on the potential of leveraging quantum computing for real-time particle track reconstruction in high-energy physics.

quant-ph↗

arXiv2012

Exploring $B_s \to D_s^{(*)\pm} K^\mp$ Decays in the Presence of a Sizable Width Difference $ΔΓ_s$

The $B_s \to D_s^{(*)\pm} K^\mp$ decays allow a theoretically clean determination of $ϕ_s+γ$, where $ϕ_s$ is the $B^0_s$-$\bar B^0_s$ mixing phase and $γ$ the usual angle of the unitarity triangle. A sizable $B_s$ decay width difference $ΔΓ_s$ was recently established, which leads to subtleties in analyses of the $B_s \to D_s^{(*)\pm} K^\mp$ branching ratios but also offers new "untagged" observables, which do not require a distinction between initially present $B^0_s$ or $\bar B^0_s$ mesons. We clarify these effects and address recent measurements of the ratio of the $B_s\to D_s^\pm K^\mp$, $B_s\to D_s^\pmπ^\mp$ branching ratios. In anticipation of future LHCb analyses, we apply the SU(3) flavour symmetry of strong interactions to convert the $B$-factory data for $B_d\to D^{(*)\pm}π^\mp$, $B_d\to D_s^{\pm}π^\mp$ decays into predictions of the $B_s \to D_s^{(*)\pm} K^\mp$ observables, and discuss strategies for the extraction of $ϕ_s+γ$, with a special focus on untagged observables and the resolution of discrete ambiguities. Using our theoretical predictions as a guideline, we make simulations to estimate experimental sensitivities, and extrapolate to the end of the planned LHCb upgrade. We find that the interplay between the untagged observables, which are accessible thanks to the sizable $ΔΓ_s$, and the mixing-induced CP asymmetries, which require tagging, will play the key role for the experimental determination of $ϕ_s+γ$.

hep-ph↗

arXiv2012

Branching Ratio Measurements of $B_s$ Decays

We have just entered an era of precision measurements for $B_s$-decay observables. A characteristic feature of the $B_s$-meson system is $B^0_s$--$\bar B^0_s$ mixing, which exhibits a sizable decay width difference. The latter feature leads to a subtle complication for the extraction of branching ratios of $B_s$ decays from untagged data samples, leading to systematic biases as large as O(10%) that depend on the dynamics of the considered decay. We point out that this effect can only be corrected for using information from a time-dependent analysis and suggest the use of the effective $B_s$ decay lifetime, which can already be extracted from the untagged data sample, for this purpose. We also address several experimental issues that can play a role in the extraction of effective lifetimes at a hadron collider, and advocate the use of the $B_s$ branching ratios, as presented in this note, for consistent comparisons of theoretical calculations and experimental measurements in particle listings.

hep-ph↗

arXiv2012

Probing New Physics via the $B^0_s\to μ^+μ^-$ Effective Lifetime

We have recently seen new upper bounds for $B^0_s\to μ^+μ^-$, a key decay to search for physics beyond the Standard Model. Furthermore a non-vanishing decay width difference $ΔΓ_s$ of the $B_s$ system has been measured. We show that $ΔΓ_s$ affects the extraction of the $B^0_s\to μ^+μ^-$ branching ratio and the resulting constraints on the New Physics parameter space, and give formulae for including this effect. Moreover, we point out that $ΔΓ_s$ provides a new observable, the effective $B^0_s\to μ^+μ^-$ lifetime $τ_{μ^+μ^-}$, which offers a theoretically clean probe for New Physics searches that is complementary to the branching ratio. Should the $B^0_s\to μ^+μ^-$ branching ratio agree with the Standard Model, the measurement of $τ_{μ^+μ^-}$, which appears feasible at upgrades of the LHC experiments, may still reveal large New Physics effects.

hep-ph↗