4/28：講演会のお知らせ (Prof. Kyungwon An 氏　(Department of Physics and Astronomy, Seoul National University))

講演題目：A photonic quantum engine driven by superradiance
講師：Prof. Kyungwon An 氏　(Department of Physics and Astronomy, Seoul National University))
日時：4月28日（金）10：00
場所：理学部本館1階 大会議室
概要：
　A superradiant
state is a special quantum state of atoms capable of producing superradiance
immediately without a time delay. We can prepare a superradiant state in an optical cavity by
exciting N atoms in the same superposition state of the ground and excited states. T hese phase
correlated atoms generate superradiance in the cavity even when the mean number of intracavity
atoms is much less than unity [J. Kim et al., Science 359, 662 (2018)]. The superradiant state has
been used to realize the long sought superabsorptio n, the opposite of superradiance, by reversing
the superradiance process in time [D. Yang et al., Nature Photonics 15, 272 (2021)]. Recently, we
have realized a photonic quantum engine, where the atoms entering the cavity are our fuel and the
photons are a n engine medium exerting radiation pressure on the mirrors. Our engine operates
between a thermal state and a superradiant state of the reservoir at the same reservoir temperature.
The effective engine temperature in the volume expansion phase rose up to 1 50,000K because of the
large ergotropy transfer from the reservoir through superradiance. The corresponding engine
efficiency was as high as 98% [J. U. Kim et al., Nature Photonics 16, 707 (2022)].

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