Quantum Enhanced Technologies

Abstract

Quantum effects have a wide variety of applications in computation, communication, and metrology. To explore practical quantum enhanced technologies, we are investigating quantum metrology in neutral atom systems, such as inertial sensors and clocks, which could revolutionize the field of precision navigation. The lower noise boundary on measurements of a two-level quantum system is given by the standard quantum limit (SQL). This limits the signal-to-noise ratio (SNR) to SNR = $\sqrt{N}$ where N is the number of atoms. Using Quantum Non-Demolition techniques (QND), it has been demonstrated that one can surpass the SQL, with the ultimate limit given by the Heisenberg Limit of SNR = N . For many implementations, this limit corresponds to an improvement by several orders of magnitude. However, achieving even the SQL is difficult in practical systems. To realize the gains of quantum enhanced metrology one must first realize high fidelity measurements of quantum systems. This fidelity is often limited by sources of technical noise in the system which must be characterized and mitigated. In this report we attempt to experimentally reach the SQL in a system of laser-cooled Rubidium 87 atoms. Atomic transitions were induced through microwave radiation and the stimulated Raman interaction. We characterize the various sources of noise that hinder the achievement of the SQL and compare our measurements to theoretical models that take these impediments into consideration. Additionally, we survey the literature for spin-squeezing techniques which allow for Heisenberg-limited measurements in similar cold-atom systems. Our investigation confirmed the difficulty of achieving even moderate amounts of squeezing for a metrologically relevant quantity. However, spin squeezing could prove to be an important technique for atom interferometry if substantial improvements in implementation are made. This work is done in collaboration with the University of New Mexico.