arXiv subjects

Romain Piron

Publications and source records attributed to Romain Piron.

5 recordsLinked to original sources

arXiv2026

Positivity in energy correlators and the event distribution formula

Energy correlators are universal observables, well defined across a wide range of theories and spacetime dimensions, from gauge theory and conformal field theory to string theory. Energy correlators are constrained by three fundamental properties: pointwise positivity of the energy flux, global positivity originating from their interpretation as state norms in a unitary theory, and energy conservation organizing multi-point energy correlators into an infinite consistent hierarchy. We argue that the most general solution to the infinite hierarchy positivity problem of energy correlators is given by the event distribution formula, which expresses energy correlators as moments of the measure on the space of probability measures on the celestial sphere. We work out in detail implications of positivity for two- and three-point energy correlators and show that it implies nontrivial two-sided bounds on their multipole expansion coefficients. The bounds obtained by requiring consistency of the infinite hierarchy of energy correlators are strictly stronger than those obtained by imposing positivity of the two- and three-point correlators alone. For the low-spin multipole coefficients studied in the paper, the derived bounds are optimal in the sense that their extrema are realized by finite mixtures of finite-particle events. We further demonstrate consequences of positivity in energy correlators in collider physics and conformal field theories.

hep-th↗

arXiv2026

Parameter Calibration for Reduced-Bandwidth Two-Photon Waveguide-QED Simulations

Waveguide-QED platforms represent one potential approach to scalable quantum technologies, but their simulation remains computationally demanding due to the large number of frequency modes required to describe traveling photons. In practice, increasing the simulated bandwidth rapidly raises the numerical cost, leading to a trade-off between accuracy and tractability. The existing approaches formulated in time-domain indirectly control this trade-off through the choice of time step, which obscures the connection between discretization parameters and the represented spectral window. In this work, we introduce an end-to-end framework to explicitly control the effective bandwidth in waveguide-QED simulations of two-photon scattering. We show that truncating the frequency domain requires consistent shifts of the model parameters, and derive a systematic calibration procedure that preserves the physical accuracy of the reduced model. This enables tuning the central frequency and the bandwidth of the numerical spectrum, leading to a several-fold reduction in the Hilbert space dimension while maintaining physical accuracy. We discuss the limitations of this calibration and relate the finite-bandwidth viewpoint to time-domain discretizations.

quant-ph↗

arXiv2026

Renormalization Treatment of IR and UV Cutoffs in Waveguide QED and Implications to Numerical Model Simulation

We present a non-perturbative, first-principles derivation of renormalization relations for waveguide-QED models, explicitly accounting for the infrared (IR) and ultraviolet (UV) cutoffs that are necessarily introduced in numerical simulations. By formulating the atomic dynamics in the time domain, we obtain explicit expressions linking the bare model parameters to the physically observable atomic frequency and decay rate, and verify their consistency with scattering theory. We further connect these results to standard Feynman diagrams, providing a transparent physical interpretation and ensuring the generality of the approach. Finally, we show how these renormalization relations can be used to parameterize simulations with a minimal frequency bandwidth, simultaneously preserving physical accuracy and reducing computational cost, thereby paving the way for efficient and reliable multi-photon light-matter simulations.

quant-ph↗

arXiv2024

Quantum Annealing for Active User Detection in NOMA Systems

Detecting active users in a non-orthogonal multiple access (NOMA) network poses a significant challenge for 5G/6G applications. Traditional algorithms tackling this task, relying on classical processors, have to make a compromise between performance and complexity. However, a quantum computing based strategy called quantum annealing (QA) can mitigate this trade-off. In this paper, we first propose a mapping between the AUD searching problem and the identification of the ground state of an Ising Hamiltonian. Then, we compare the execution times of our QA approach for several code domain multiple access (CDMA) scenarios. We evaluate the impact of the cross-correlation properties of the chosen codes in a NOMA network for detecting the active user's set.

quant-ph↗

arXiv2024

Scheduling Quantum Annealing for Active User Detection in a NOMA Network

Active user detection in a non-orthogonal multiple access (NOMA) network is a major challenge for 5G/6G applications. However, classical algorithms that can perform this task suffer either from complexity or reduced performances. This work aims at proposing a quantum annealing approach to overcome this trade-off. Firstly, we show that the maximum a posteriori decoder of the activity pattern of the network can be seen as the ground state of an Ising Hamiltonian. For N users in a network with perfect channels, we propose a universal control function to schedule the annealing process. Our approach avoids to continuously compute the optimal control function but still ensures high success probability while demanding a lower annealing time than a linear control function. This advantage holds even in the presence of imperfections in the network.

eess.SP↗