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

量子技术有望给数据处理、通信和计量带来革命性的变化。目前解锁这一潜力的方法建立在可扩展和完全连贯的设备上。尽管量子路线图目前已经制定，纠错等要素的必要性也得到了理解，但目前尚不清楚所需的技术突破是否真的完全可以实现。这个项目遵循一条新的路线，试图通过利用开放系统中的集体现象来识别和实现产生可能的量子优势的量子资源。这种方法的好处是，它从一开始就不依赖于完美的连贯性。相反，它利用了相干相互作用和耗散过程之间的竞争，这有望产生一定程度的对外部扰动的稳健性。一个突出的例子是所谓的耗散时间晶体，它构成了一个多体相，显示出持续的和明确定义的时间振荡，尽管它们的动力学演化受到非相干过程的严重影响。这个项目的目标是更普遍地识别和描述这种多体阶段，并进行原则证明实验，以证明它们在传感和计时协议中的适用性。我们的重点将放在自旋-玻色子模型上，它构成了简单但基本且广泛相关的多体量子系统。在我们的联盟中，我们将使用囚禁离子的晶体来实现这样一个系统，这种晶体为单独可寻址的量子粒子提供超长寿命和与状态无关的高保真限制。晶体振动调节颗粒之间的相互作用，并允许就地冷却。后者是必不可少的，因为只有这种能力才能实现耗散多体相的长期稳定和连续读出。除了按需生成量子资源的能力外，这个高度可控的平台还允许我们解决一系列重要的基本问题，从周期性驱动下开放量子多体动力学的一致公式到使用(时延)反馈来控制耗散动力学。为了实现这一雄心勃勃的议程，我们将结合各种理论技术，包括分析方法、基于张量网络的数值模拟、量子轨迹分析和受机器学习启发的参数估计方法。所有这些都将在我们不同的跨学科联盟内实现，该联盟聚集了开放量子系统理论、量子光学和凝聚态物理以及实验囚禁离子物理方面的专家。

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.