An atomic cell includes a pair of windows, and a body disposed between the pair of windows and forming an inner space in which alkali metal atoms are sealed along with the pair of windows. The inner space has a longitudinal shape in which a cross-section perpendicular to an arranging direction of the pair of windows extends in a first direction. Further, when a length of the inner space in a second direction perpendicular to the first direction in the cross-section is set to L1, and a length of the inner space in the first direction is set to L2, a relationship of L2/L1≧1.1 is satisfied.
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