Sensitivity of a collisional single-atom spin probe

TL;DR

This paper investigates the steady-state sensitivity of a single-atom quantum probe in ultracold gases, revealing optimal parameter regions and connecting microscopic interactions to thermodynamic properties for improved sensing.

Contribution

It provides a numerical analysis of the steady-state sensitivity maxima of a collisional single-atom probe, linking microscopic spin-exchange dynamics to thermodynamic sensing capabilities.

Findings

Sensitivity maxima occur at specific (B, T) parameters.

Sensitivity is highest when sensing the energy ratio between thermal and Zeeman energies.

Qualitative agreement between equilibrium and nonequilibrium sensitivity patterns.

Abstract

We study the sensitivity of a collisional single-atom probe for ultracold gases. Inelastic spin-exchange collisions map information about the gas temperature T or external magnetic field B onto the quantum spin-population of single-atom probes, and previous work showed enhanced sensitivity for short-time nonequilibrium spin dynamics [1]. Here, we numerically investigate the steady-state sensitivity of such single-atom probes to various observables. We find that the probe shows distinct sensitivity maxima in the (B, T ) parameter diagram, although the underlying spin-exchange rates scale monotonically with temperature and magnetic field. In parameter space, the probe generally has the largest sensitivity when sensing the energy ratio between thermal energy and Zeeman energy in an externally applied magnetic field, while the sensitivity to the absolute energy, i.e., the sum of kinetic and Zeeman energy, is low. We identify the parameters yielding sensitivity maxima for a given absolute energy, which we can relate to a direct comparison of the thermal Maxwell-Boltzmann distribution with the Zeeman-energy splitting. We compare our equilibrium results to nonequilibrium experimental results from a single-atom quantum probe, showing that the sensitivity maxima in parameter space qualitatively prevail also in the nonequilibrium dynamics, while a quantitative difference remains. Our work thereby offers a microscopic explanation for the properties and performance of this single-atom quantum probe, connecting thermodynamic properties to microscopic interaction mechanisms. Our results pave the way for optimization of quantum-probe applications in (B, T ) parameter space beyond the previously shown boost by nonequilibrium dynamics.