"The advent of laser cooling and manipulation techniques at the single atom level has opened the door to the realization of controllable, idealized many-body systems, which in many cases constitute physical realization of toy-models. A successful and popular approach is to engineer cold dilute gases of mesoscopic size whose atoms can be spatially ordered with light beams to mimic condensed matter systems. Recreating the essence of a complex quantum system in a simpler quantum system to let nature ""compute"" the output is the basis of quantum simulation. This approach is extremely beneficial for systems of more than a few interacting atoms where in many cases no ab initio calculation is possible, even in simplified models. In this context much effort has been put into a variety of problems that are intractable by classical computation (e.g. quantum magnetism, quantum phase transition, frustrated systems, spin glasses, superconductivity and topological phases). One of the most intriguing open question in quantum many-body physics is how and under what circumstances a system evolves into thermal equilibrium. This fundamentally important problem has very recently received a surge of attention and the approach to equilibrium (or the absence of it) is the subject of a number of current experimental and theoretical efforts.
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."
