A Simulation Framework for Ramsey Interferometry

TL;DR

This paper introduces a comprehensive simulation framework combining optics, magnetic fields, and spin dynamics to optimize Ramsey interferometry experiments, with applications to axion-like particle searches at the ESS.

Contribution

A novel integrated simulation framework that models optics, magnetic environments, and spin dynamics for Ramsey interferometry experiments.

Findings

Improved spin flip angle precision from 0.67 to 0.17 radians.

Enhanced phase sensitivity by a factor of 4.

Application to design experiments at the European Spallation Source.

Abstract

The sensitivity of Ramsey interferometry experiments is governed by the interplay between the beam phase-space distribution and the magnetic field environment through which the spins propagate. Quantitative optimisation thus requires a consistent treatment of optics, magnetics and spin dynamics. We present a simulation framework that enables such an analysis by combining neutron optics simulations in McStas, magnetic field modelling in COMSOL and spin-dynamics simulation in the new RamseyProp program. We describe how important experimental parameters such as adiabaticity, flip angle distributions and Ramsey fringe contrast can be studied. The code is being applied to design an experiment to search for axion-like particles at the European Spallation Source (ESS). We examine how the pulsed time structure of the ESS can be exploited to perform Ramsey interferometry on a broad neutron velocity spectrum. In the absence of velocity or timing restrictions, the standard deviation of the spin flip angle at zero detuning can be reduced from 0.67 to 0.17 radians using time-dependent amplitude modulation. Similarly, the phase sensitivity can be improved by a factor of 4 for a 10 m long setup starting 15 m from the ESS moderator.