BEGIN:VCALENDAR VERSION:2.0 PRODID:Icfo X-PUBLISHED-TTL:P1W BEGIN:VEVENT UID:69e88edc5defd DTSTART:20220929T120000Z SEQUENCE:0 TRANSP:OPAQUE LOCATION:ICFO Auditorium and Online (Teams) SUMMARY:ICFO | CHARIKLEIA TROULLINOU CLASS:PUBLIC DESCRIPTION:This thesis describes experiments that employ squeezed light to improve the performance of a sensitive optically-pumped magnetometer (OPM ). The squeezed light source employs parametric amplification of vacuum fl uctuations to produce squeezed vacuum and polarization-squeezed light tuna ble around the Rb D1 line. The OPM employs Bell-Bloom Optical pumping of a high density vapor (with atom number density 10^{13}) and paramagnetic Fa raday rotation\, also on the Rb D1 line. The setup allows convenient switc hing from probing with laser light to probing with polarization-squeezed l ight\, to study the use of the latter in atomic magnetometry.\nThe magneto meter shows sub-pT/Hz^{1/2} sensitivity\, limited by quantum noise\; spin projection noise at low freqü\;è\;ncies (<\;100Hz) and photon shot noise at high frequencies. Probing with polarization squeezed light s uppresses the photon shot\nnoise by 2dB\, limited by the available squeezi ng and optical losses in passing through the vapor. This shot-noise suppre ssion improves the high-frequency sensitivity and increases the measuremen t bandwidth\, with no observed loss ofsensitivity at any frequency. This r esult confirms experimentally the expected evasion of measurement back-act ion noise in the Bell-Bloom magnetometer.\nThe thesis also develops a phys ical model to explain the observed spin dynamics of the Bell-Bloom magneto meter. The model describes the combined spin and optical polarization dyna mics using Bloch equations with stochastic drive and\ndetection noise term s. A perturbative approach and Fourier methods are then used to obtain ana lytic expressions for the magnetometer's frequency response\, spin project ion noise and photon shot noise. The role of measurement back-action emerg es from a study of this model. As polarization squeezing reduces optical n oise in the detected Stokes parameter\, the accompanying ellipticity anti- squeezing is shunted into the unmeasured spin component.\nThe thesis also reports a study of squeezed-light-enhanced magnetometry at a range of atom ic densities\, from 2.18 10^{12} atoms/cm3 to 1.13 10^{13} atoms/cm3 . Ope rating with fixed conditions of optical pumping\, the signal amplitude\, i nstrument noise spectrum and magnetic resonance width are measured as a fu nction of atomic number density\, for both laser- and squeezed-light probi ng. The equivalent magnetic noise spectra are then calculated. In the phot on-shot-noise-limited portion of the spectrum\, the squeezed light probing improves the magnetometer's sensitivity and measurement bandwidth for the full range of atomic density values. In particular\, the laser-probed mag netometer shows a sensitivity optimum at n ~ 6 10 ^{12} atoms/cm3\, and th e squeezed-light-probed magnetometer surpasses this sensitivity.\nThe thes is concludes with a discussion of the potential of stronger optical squeez ing to enhance the instrument's sensitivity in different portions of the s pectrum. Using the theory model we estimate the enhancement of the equival ent magnetic noise spectrum for 2 dB \, 5.6 dB and perfect squeezing (zero noise in the detected polarization component) at the input to the atomic medium.\n \;\nThesis Director: Prof Dr. Morgan Mitchell DTSTAMP:20260422T090324Z END:VEVENT END:VCALENDAR