Thesis Submission

In the pursuit of higher precision in the field of metrology, one seeks to exploit the fundamental principles of quantum mechanics, giving rise to the field of quantum sensing. This thesis explores quantum sensing and quantum non-demolition (QND) measurement techniques using both thermal and ultracold atomic systems.
 

First, we investigate the use of spin noise spectroscopy (SNS) as a minimally invasive probe of atomic spin fluctuations, enabling real-time and non-perturbative measurements of magnetic fields and spin dynamics. Building upon this concept, we develop a Raman-driven spin noise spectroscopy (RDSNS) scheme that enhances spin noise signals by several orders of magnitude, allowing detailed studies of dynamical spin properties. Using this approach, we realize a highly sensitive, broadband atomic magnetometer that overcomes the limitations of conventional atomic magnetometers.
 

We further extend these methods to probe cold atomic systems. In particular, we construct a dual-species sodium–potassium three-dimensional magneto-optical trap to study intra- and inter-species interactions. Using the RDSNS technique, we perform minimally destructive, real-time density measurements that are not accessible with conventional destructive imaging methods such as absorption and fluorescence imaging. Such a non-invasive density probe is essential for studying dynamically evolving cold atomic clouds and density wave formation, with potential applications in diverse areas including quantum transport and quantum information.
 

In addition, we explore the generation of multiple spin noise peaks arising from long-range coherences between multiple Zeeman states. These harmonics are extremely sensitive to changes in the external magnetic field, making them promising candidates for enhancing magnetic field detection sensitivity.
 

Overall, these results represent a significant step toward non-demolition probing of quantum systems and pave the way for next-generation quantum sensors and precision measurement technologies.