Non-monochromatic optical pumping in spin-based quantum sensors

Anton K. Vershovskii, Sergei P. Dmitriev, G. G. Kozlov +2 more

Abstract The principal limitations imposed by spin (or atomic) quantum projection noise on the sensitivity of optical quantum sensors on thermal atoms, which include frequency standards, magnetometers, and gyroscopes that use optical detection of electron paramagnetic resonance, have been theoretically and experimentally studied. The effect of increasing the rms amplitude of the projection noise in a magnetometric scheme under the influence of a strong optical pumping has been demonstrated. Its explanation has been proposed and experimentally confirmed: it has been shown that this effect is explained by the invariance of the integral power of projection noise in relation to the magnetic resonance linewidth in a wide range of pumping intensities An experimental study of the parameters of projection noise in a magnetometric quantum sensor has been conducted and recommendations for optimizing the sensor parameters have been given.

Claude N. Cohen-Tannoudji

A. F. Sousa, C. H. S. Vieira, H. M. Florez

Optically Pumped Magnetometers use light to drive an atomic vapor into a Non-Equilibrium Steady State for sensing. This kind of state is achieved when spin-exchange collisions, together with optical pumping, dominate the relaxation dynamics, redistributing the atomic populations and thereby shaping the steady-state configuration. Despite the rapid advancement of atomic magnetometer technology, a comprehensive thermodynamic analysis of the state preparation is largely unexplored. We apply a thermodynamic framework to alkali atoms in a vapor cell, modeling their interactions with the pump laser and their relaxation via spin-exchange and spin-destruction collisions. We analyze how the pump rate and light polarization determine the non-equilibrium steady state, quantifying irreversibility via entropy production, assessing useful energy via ergotropy, and defining the spin-polarization efficiency. Finally, we establish a connection between metrological performance and the Quantum Fisher Information (QFI), demonstrating that a higher thermodynamic efficiency directly translates into an improved fundamental bound on magnetometer sensitivity. These results provide insights for optimizing state preparation in quantum sensors.

G. Caimi

Anton K. Vershovskii, С.П. Дмитриев, Г.Г. Козлов +2 more

The paper theoretically and experimentally investigates the fundamental limitations imposed by spin (or atomic) quantum projection noise on the sensitivity of optical quantum sensors based on thermal atoms (this class of devices includes frequency standards, magnetometers, and gyroscopes using optical detection of electron paramagnetic resonance). The effect of increasing the rms amplitude of the projection noise in the magnetometric scheme under the influence of strong optical pumping is demonstrated, its explanation is proposed and experimentally tested - it is shown that in a wide range of pump intensities this effect is explained by the invariance of the projection noise integral power with respect to the magnetic resonance line width. An experimental study of the parameters of projection noise in a magnetometric quantum sensor was carried out, recommendations were given for optimizing the sensor parameters.

Daniel F. Walls, Gerard J Milburn