Signs of a ‘Time Crystal’ in a Surprising Place
The periodic spatial arrangement of atoms in a crystal like NaCl has been known for a century. The concept of a “time crystal” is a much more recent development, just ~8 years old. About 4 years ago, theorists predicted the existence of a Floquet/discrete time crystal (DTC), a prototypical example of a novel phase of matter that awaits discovery in many-body systems driven out of equilibrium. Thus, it was exciting when in 2017, independent experiments using ion traps and diamond NV centers both reported that they had found signatures of the DTC. Here, we present nuclear magnetic resonance (NMR) observations of DTC signatures in a third, strikingly different system: an ordered spatial crystal of ammonium dihydrogen phosphate (ADP). We will explain how we accidentally ended up probing a new corner of parameter space, and why our results appear to challenge earlier assumptions about the conditions needed for DTCs to form. Moreover, we will describe how we expanded the NMR toolbox to develop a novel DTC-echo, revealing the hidden coherence produced by the DTC sequence. The twists and turns that led to these serendipitous discoveries are well described by Louis Pasteur’s quote: “chance favors the prepared mind”.
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