Ultimate limits of exoplanet spectroscopy: A quantum approach

One of the big challenges in exoplanet science is to determine atmospheric makeup extrasolar planets, and find biosignatures that hint at existence biochemical processes on another world. The biomarkers we are trying detect gases atmosphere like oxygen or methane, which have deep absorption features visible near-infrared spectrum. Here establish ultimate quantum limit for determining presence absence a spectral line, dim source much brighter stellar source. We characterise associated error exponent both frameworks symmetric asymmetric hypothesis testing. found structured measurement based spatial demultiplexing allows us decouple light coming from planet achieve limits. If has intensity $\epsilon \ll 1$ relative star, show this approach significantly outperforms direct spectroscopy yielding an improvement by factor $1/\epsilon$. optimal measurement, combination interferometric techniques spectrum analysis.