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team — A veritable tour-de-force in metrology reported last year by physicists at the Laboratory for Attosecond Physics (LAP), which is jointly run by LMU Munich and the Max Planck Institute for Quantum Optics (MPQ), has been accepted as a new world record by the Guinness Book of Records. In 2016, an LAP research team led by Dr. Martin Schultze succeeded in measuring the duration of a specific physical phenomenon induced by the interaction of light with atoms to an accuracy of 850 zeptoseconds. You may well ask, how long is a zeptosecond? A zeptosecond is equivalent to 10-21 sec or, to put in the rather more cumbersome, lexical form – a trillionth of a billionth (one sextillionth!) of a second. The feat achieved by Schultze and colleagues is the most precise measurement yet made in the time domain of a defined event in the microcosmos. In addition, it constitutes the first absolute determination of the dynamics of ‘photo-ionization’. The term refers to the process which leads to the ejection of electrons from atoms following excitation by photons with a certain minimum energy. This phenomenon (also known as the photoelectric effect) was predicted on theoretical grounds by Albert Einstein in 1905, and confirmed experimentally a short time later. However, only in recent years has it become possible to experimentally determine the time that elapses between the arrival of the photon and the expulsion of the free electron. In a paper published in 2010 (Science, 25 June 2010), physicists at the LAP showed that the whole process takes from 5 to 15 attoseconds (1 as lasts for 10-18 sec), depending on the energy of the incoming photon. They have now pinned down the value of this energy-dependent parameter to within 850 zs, which represents a previously unattainable precision for a timing measurement – as has now been acknowledged by its inclusion in the latest edition of the Guinness Book of Records. The study itself appeared in the leading journal Nature Physics (7. November 2016).