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arXiv · 1501.00346

Quantum-Limited Spectroscopy

Gar-Wing Truong·James D. Anstie·Eric F. May·Thomas M. Stace·Andre N. Luiten
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Abstract

Spectroscopy has an illustrious history delivering serendipitous discoveries and providing a stringent testbed for new physical predictions, including applications from trace materials detection, to understanding the atmospheres of stars and planets, and even constraining cosmological models. Reaching fundamental-noise limits permits optimal extraction of spectroscopic information from an absorption measurement. Here we demonstrate a quantum-limited spectrometer that delivers high-precision measurements of the absorption lineshape. These measurements yield a ten-fold improvement in the accuracy of the excited-state (6P$_{1/2}$) hyperfine splitting in Cs, and reveals a breakdown in the well-known Voigt spectral profile. We develop a theoretical model that accounts for this breakdown, explaining the observations to within the shot-noise limit. Our model enables us to infer the thermal velocity-dispersion of the Cs vapour with an uncertainty of 35ppm within an hour. This allows us to determine a value for Boltzmann's constant with a precision of 6ppm, and an uncertainty of 71ppm.

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Gar-Wing Truong, James D. Anstie, Eric F. May, Thomas M. Stace, Andre N. Luiten. 2015-01-02. Quantum-Limited Spectroscopy. https://arxiv.org/abs/1501.00346

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