Squeezing and entanglement play crucial roles in quantum metrology. Yet, achieving entanglement is challenging in systems with large atom number where higher absolute sensitivities are expected. I will review our experiment results on how to create squeezed atomic spin state for 10^11 atoms, and how to employ it for weak magnetic field sensing. In parallel, photon shot noise constitutes fundamental limits in optical measurements. We study the interplay of quantum optical noises and the measurement process, and demonstrate squeezed light can be self-generated during sensing to overcome the quantum limit. Furthermore, simultaneous quantum squeezing of the atomic spin and the light is produced for better suppression of quantum noises. Finally, a personal view on routes to “quantum supremacy” in quantum metrology will be given.

Please contact phweb@ust.hk should you have questions about the talk.