A temperature probe for the ultracold

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Science  13 Feb 2015:
Vol. 347, Issue 6223, pp. 733
DOI: 10.1126/science.347.6223.733-g

The temperature of an everyday macroscopic object is well understood and easy to measure. The concept of temperature, however, becomes blurry when the number of particles in a system becomes so small that the ensemble breaks down into a number of individual components, such as for atoms or molecules trapped in an optical lattice and cooled to ultralow temperatures. McDonald et al. demonstrate a spectroscopic technique that uses the line shift and change in the line shape of an atomic or molecular transition to determine the temperature of trapped atoms or molecules down to nanokelvin temperatures. This technique should prove useful in a range of applications, including metrology and probing the energetic dynamics of ultracold chemical reactions.

Phys. Rev. Lett. 114, 23001 (2015).

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