Electric field sensing near the surface microstructure of an atom chip using cold Rydberg atoms

摘要

This thesis reports experimental observations of electric fields using Rydberg atoms, including dc field measurements near the surface of an atom chip, and demonstration ofmeasurement techniques for ac fields far from the surface. Associated theoretical resultsare also presented, including Monte Carlo simulations of the decoherence of Rydberg statesin electric field noise as well as an analytical calculation of the statistics of dc electric fieldinhomogeneity near polycrystalline metal surfaces.DC electric fields were measured near the heterogeneous metal and dielectric surface ofan atom chip using optical spectroscopy on cold atoms released from the trapping potential.The fields were attributed to charges accumulating in the dielectric gaps between the wireson the chip surface. The field magnitude and direction depend on the details of the dcbiasing of the chip wires, suggesting that fields may be minimized with appropriate biasing.Techniques to measure ac electric fields were demonstrated far from the chip surface,using the decay of a coherent superposition of two Rydberg states of cold atoms. We haveused the decay of coherent Rabi oscillations to place some bounds on the magnitude andfrequency dependence of ac field noise.The rate of decoherence of a superposition of two Rydberg states was calculated withMonte Carlo simulations. The states were assumed to have quadratic Stark shifts and thepower spectrum of the electric field noise was assumed to have a power-law dependenceof the form 1/f^κ. The decay is exponential at long times for both free evolution of thesuperposition and and Hahn spin-echo sequences with a π refocusing pulse applied toeliminate the effects of low-frequency field noise. This decay time may be used to calculatethe magnitude of the field noise if κ is known.The dc field inhomogeneity near polycrystalline metal surfaces due to patch potentialson the surface has been calculated, and the rms field scales with distance to the surface as1/z^2. For typical evaporated metal surfaces the magnitude of the rms field is comparableto the image field of an elementary charge near the surface.