Appreciating the classical elegance of time crystals

ScienceDaily | 9/19/2019 | Staff
In a crystal, atoms are highly ordered, occupying well-defined locations that form spatial patterns. Seven years ago, the 2004 Physics Nobel laureate Frank Wilczek pondered the possibility of a 'time analogue of crystalline spatial order' -- systems that display sustained periodic temporal modulations in their lowest-energy state. The concept of such structures with an oscillating ground state is highly intriguing. Alas, not long after the idea has been published, it was proven that such time crystals are not possible without breaking fundamental laws of physics. Not all was lost, though. Subsequent theory work suggested that when quantum many-body systems are periodically driven, then new persistent time correlations emerge that are evocative of Wilczek's time crystals. These driven systems were dubbed 'discrete time crystals', and in 2017 the first experimental realizations of such states were reported in ensembles of coupled particles (ions, electrons and nuclei) that display quantum-mechanical properties.

Before long, astute observers spotted distinct similarities between discrete time crystals in quantum systems and so-called parametric resonators, a concept in classical physics reaching back to work by Michael Faraday in 1831. The connection between these two bodies of work remained, however, opaque. Now, a new framework goes a long way towards lifting the ambiguities surrounding the similarities between periodically driven classical and quantum systems. Writing in an article published today in the journal Physical Review Letters, Toni Heugel, a PhD student in the Department of Physics at ETH Zurich, and Matthias Oscity, a Master student there, working with Dr. Ramasubramanian Chitra and Prof. Oded Zilberberg form the Institute for Theoretical Physics and with Dr. Alexander Eichler from the Laboratory for Solid State Physics, report theoretical and experimental work that establishes how discrete time crystals can be generated that, on the one hand, require no quantum mechanical effects and, on the other hand,...
(Excerpt) Read more at: ScienceDaily
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