Collective quantum phenomena in dissipative systems - towards time-crystal applications in sensing and metrology

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Quantum technology carries the promise to revolutionise data processing, communication, and metrology. The current approach towards unlocking this potential builds on scalable and fully coherent devices. Although a quantum roadmap is currently set out and the necessity of elements such as error correction is understood, it is currently unclear whether the required technological breakthroughs are indeed fully achievable. This project follows a novel route and seeks to identify and realise quantum resources yielding a possible quantum advantage by exploiting collective phenomena in open systems. The benefit of this approach is that it does not rely on perfect coherence from the outset. Instead, it exploits the competition between coherent interactions and dissipative processes, which is expected to yield a certain degree of robustness against external perturbations. A prominent example are so-called dissipative time-crystals, which constitute a many-body phase that displays persistent and well-defined temporal oscillations although their dynamical evolution is heavily influenced by incoherent processes. The goal of this project is to identify and characterise such many-body phases more generally and to perform proof-of-principle experiments that demonstrate their applicability in protocols for sensing and timekeeping. Our focus will be on spin-boson models which constitute simple, yet fundamental and broadly relevant, many-body quantum systems. Within our consortium we will implement such a system using crystals of trapped ions, which offer ultra-long-lived and state-independent hi-fidelity confinement of individually addressable quantum particles. Crystal vibrations mediate interactions among the particles and allow in-situ cooling. The latter is indispensable as only this capability will allow long-time stability and continuous read-out of dissipative many-body phases to be achieved. Apart from its capability to generate quantum resources on demand this highly controllable platform allows us to address a spectrum of important foundational questions, ranging from the consistent formulation of open quantum many-body dynamics under periodic driving to the use of (time-delayed) feedback for controlling dissipative dynamics. To accomplish this ambitious agenda, we will combine various theoretical techniques including analytical approaches, tensor-network-based numerical simulations, quantum trajectory analyses and machine learning-inspired methods for parameter estimation. All this will be achieved within our diverse and interdisciplinary consortium which gathers experts on the theory of open quantum systems, quantum optics and condensed matter physics as well as in experimental trapped ion physics.