Abstract
Trapped ultracold gases are highly controllable experimental systems with unique quantum properties, making them a brilliant medium for research in solid state physics, quantum computation, and precision measurements. The standard technique for observing a cold atomic sample is time-of-flight absorption imaging. While this provides valuable information regarding the distribution and quantum state of atoms, the process destroys the sample via spontaneous emission and recoil heating, allowing for acquisition of just one data point per experimental run. In this thesis we develop and implement a complementary hyperfine state sensitive, off-resonant, optical dispersive interrogation system that uses frequency modulation spectroscopy to monitor the temporal dynamics of atomic population during coherent dynamical processes in cold atom systems. The applicability of this robust and powerful tool is expanded to simultaneously measure both the F = 2 hyperfine state population of 87Rb and the F = 9/2 hyperfine state population of 40K. This dual-species probe is used to monitor the sympathetic cooling process, whereby 40K is cooled indirectly via collision with a sample of 87Rb, which itself is undergoing forced RF evaporative cooling.
The dispersive probing technique is then used to investigate a range of magnetic Feshbach resonances in 87Rb. Feshbach resonances allow the atomic interaction strength to be precisely tuned via an external magnetic field. Rapid and effcient location and identification of four such resonances were demonstrated between the |F=1, mF=1> and |F=2, mF=0> states. Despite the resonance-induced loss features being <~0.1 G wide, only a small number of experimental runs was sufficient to explore a magnetic field range >18 G. The resonances consist of two known s-wave features in the vicinity of 9 G and 18 G, and two previously unobserved p-wave features near 5 G and 10 G. The dispersive detection approach is further used to monitor the atomic loss in real-time, and directly characterise the two-body loss dynamics for each Feshbach resonance. We further characterise the four observed Feshbach resonances by dispersively measuring the 2-body loss rate coefficient, K21, as a function of magnetic field.
Finally, the dispersive probe method is paired with an FPGA-based feedback algorithm and used to perform reliable transfer of 87Rb atoms to a target quantum state in the presence of an unknown, random magnetic field. The algorithm processes off-resonant optical measurements of state populations during a microwave-induced adiabatic rapid passage in real time, and terminates the process when a certain threshold in population transfer is achieved.