For a long time, it was believed that the realization of quantum technologies such as quantum computing or quantum-enhanced sensing would require to isolate quantum systems perfectly from their environment. However, in recent years it has become evident that dissipation in a quantum system by coupling to an external reservoircan actually have the reverse effect of steering the system into interesting and useful quantum many-body states. This resulted in a desire to develop a deeper understanding of such open quantum many-body systems, both on a fundamental level and also in terms of their technological applications. Strikingly, these two directions are inherently linked. I will present how a better understanding of dissipative phase transitions in terms of a variational principle  enables the realization of a dissipative quantum sensor with extraordinary properties .
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 M. Raghunandan, J. Wrachtrup, H. Weimer, PRL 120, 150501 (2018)