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Frontiers of Quantum Atom-Light Interactions

Periodic Reporting for period 3 - FoQAL (Frontiers of Quantum Atom-Light Interactions)

Reporting period: 2018-03-01 to 2019-08-31

The key to the success of atomic physics and quantum optics relies on our understanding and ability to control the way that light and matter interact with each other at the level of their constituent particles – single atoms and photons. From fundamental tools such as laser cooling and trapping or cavity quantum electrodynamics come potentially powerful applications ranging from the study of many-body systems (“quantum simulation”) using ultracold atoms to quantum atom-light interfaces for quantum information processing and quantum networks. However, these same techniques have clear limitations or tradeoffs, which preclude many parameter regimes or paradigms for the utilization of cold atoms, and which constitute bottlenecks for further progress.

Separately, in recent years, groups worldwide have succeeded in interfacing cold atoms with micro- and nano-photonic systems, with a primary goal of improving the figures of merit and scalability of their macroscopic counterparts. However, while the direct transfer of paradigms from macroscopic to nanoscopic systems might increase figures of merit, it results in no fundamentally new functionalities. Within this context, FoQAL pursues a dramatic and powerful new vision of what can be achieved with nanophotonic systems. Exploiting unique features such as control over the dimensionality and dispersion of light, the engineering of quantum vacuum forces, and the strong optical fields and forces associated with confining light to the nanoscale, we will completely re-define our understanding of the ways in which light and matter can interact at the quantum level. We will develop fundamentally new paradigms for atomic trapping, tailoring atomic interactions, and quantum nonlinear optics that are not bound by previous limits, and which cannot be duplicated in macroscopic systems even in principle.
One of the main initial challenges in theoretically understanding the emerging atom-nanophotonics interfaces is that many of the systems do not obviously fit into previously established models for quantum atom-light interactions. Within this context, we have developed a novel and universal formalism capable of describing atom-light interactions in complex dielectric settings. On one hand, this so-called quantum “spin model” has been crucial to understanding and modeling the first experiments in the world that observe atomic interactions in photonic crystal waveguides. On the other hand, it has been used to theoretically predict new and exotic phenomena that should be realizable with such systems, such as the formation of molecules of photons, or “quantum crystallization,” in which entanglement between atomic internal degrees of freedom are responsible for the formation and stabilization of spatial order.

Furthermore, due to its universal nature, the spin model can even be used to provide new insights into “conventional” atomic systems, such as free-space ensembles. As one remarkable example, we have used this model to predict a new maximum bound on the performance of a quantum memory for light, which is exponentially better than a bound that was previously thought to be fundamental.
The fact that the spin model, described above, predicts an exponential improvement in an application for atom-light interfaces than was previously known, invites a broad re-examination of the true capabilities of such systems. It certainly suggests that some of the fundamental and historic assumptions regarding atom-light interactions can be dramatically violated, and offers a fascinating opportunity to “re-invent” the rules of such systems and search for enhanced possibilities over a broad set of applications involving atoms and light.