Figure 1

(a) Schematic representation of the experimental configuration. A laser beam is linearly polarized and sent through a magnetically shielded uncoated heated Cs cell in a magnetic field. The beam is split on a PBS according to the orientation of the \(\lambda /2\) plate and recorded by a balanced polarimeter, after which the signal is sent to post processing. (b) Examples of recorded spin noise power spectral densities (PSD) at \(\nu _{L} = 510\text{ kHz}\) in the absence of a magnetic field gradient (blue) and in a high gradient (red) (\({\mathrm{d}} B_{z} / {\mathrm{d}} y \approx 1.3\text{ mT/m}\)). (c) Polarimeter output signal; the red vertical dashed line separates the cases where the spin noise is absent (left) and when it is present (right). The red horizontal lines correspond to \(\pm 5\sigma_{bg}\) where \(\sigma_{bg}\) is the standard deviation of photon shot noise and electronic noise of the measurement system. The QCNR is \(\sigma_{s}/\sigma_{bg} \approx 3.16\) where \(\sigma_{s}\) corresponds to the standard deviation of the signal with spin noise. LP, linear polarizer; \(\uplambda /2\), half-wave plate; B, magnetic field; PBS, polarizing beam splitter; A, attenuator; PD, photodiode