Periodic Reporting for period 2 - MADAME (Mesoscopic lAttices of ryDbergs for quAntuM thErmalization)
Reporting period: 2018-11-01 to 2019-10-31
The aim of this proposal is therefore to answer: under what conditions does a quantum system thermalize?
This broad question is divided here into two aspects, each focused on a precise goal within the Fellowship. The outgoing phase, corresponding to the first period reported here, addressed the compelling phenomenon of thermalizationin in the presence of a strong coupling to the environment. It was hosted by Prof. Porto, from the Laser Cooling and Trapping (LCT) group led by W.D. Phillips at the Joint Quantum Institute (JQI), Gaithersburg/College Park, Maryland, USA. The JQI is an institution joining the National Institute for Standards and Technology (NIST) and the University of Maryland (UMD) and research was conducted at both sites. The group owns a powerful quantum simulation apparatus consisting of a double-well optical lattice for Rubidium87 where single atoms can be localized to lattice sites. This forms an excellent experimental platform for our quantum dissipative studies. We started with strongly-interacting, dissipative Rydberg atoms pinned to the optical lattice and excited for many Rydberg lifetimes, so as to study the long time limit of an initially-ordered, strongly interacting dissipative system. We discovered a spontaneous mechanism of collective dephasing, valid whenever many rydberg atoms interact strongly. This is an important contribution for coherent control, because it imposes an upper limit on the size of quantum simulators based on rydberg interactions, and explains the difficulties observed around the world with dense samples.
This Grant included a short post-doctoral internship in the team of Tilman Esslinger at the Eidgenössische Technische Hochschule Zürich (ETHZ), Switzerland, where I went from April to June 2017. This internship allowed me to acquire the skills necessary to add a new component to the JQI experiment: Floquet engineering. With it, we found a new type instability based on non-equilibrium collective dynamics, which amounts to heating the atoms to infinite temperature.
In the incoming phase at the Laboratoire Charles Fabry, Palaiseau, France, we worked on a quantum simulation experiment based on a small number of individually trapped rydberg atoms. We developed a new laser trapping scheme for rydberg states, and studied non-trivial topological states with few atoms.
In total, this 3-years MSCA grant produced 5 papers in international refereed journals and as many conference proceedings."
We then switched direction in favor of the new system, which does not rely on Rydberg atoms. We used ground-state atoms coupled to the environment via an external drive. The drive consists in periodically modulating the optical lattice position (“shaking” the lattice). This opens the question of heating, as energy can be absorbed from the drive, which is crucial for the novel field of Floquet engineering. Theory predicts heating to infinite temperature under most (but not all) conditions, and the mechanism is not completely understood. In particular, recent theoretical predictions dating from about the Action’s starting date expect the excitation spectrum of a condensate under periodic driving to become unstable, leading to yet-unobserved parametric instabilities in bosonic Floquet systems. We directed our research towards understanding the heating mechanism and experimentally testing this prediction. This required the innovation of new experimental techniques for precise shaking and heating rate measurements, and resulted in several articles (1 published, 1 under review).
In the second period, small systems were considered. We first developed new tools for controlling individual rydberg atoms, then applied them to the study of non-trivial artificial systems supporting intrinsic spin-orbit coupling. This resulted in 2 articles (1 accepted, 1 under review).
The results from the second (IOGS) part are important, both from an application and fundamental perspective. The first expands the quantum simulation toolbox, which is an important strategic point for future quantum technologies. The second achievement is fundamentally important since intrinsic spin-orbit coupling is naturally present in complex quantum matter, and being able to re-create it in a controlled artificial setting is a crucial step for future quantum engineering of robust complex states, as well as our fundamental understanding.