LPTMS Internship Proposal: Self-assembly in space and time

Contact: Martin Lenz

Recent experimental developments have made assembling machines at the nanometer scales that mimic or even attempt to surpass the functions of biological objects an increasingly reasonable goal (see https://www.nobelprize.org/prizes/chemistry/2016/summary/). Despite remarkable progress in manufacturing individual nanometer-sized objects with controlled shapes however (see an example in the illustration), assembling many of them into larger structures remains an open challenge and an active field of research.
In this project we will undertake an additional challenge, namely to self-assemble such objects not only in space, but also in time. Specifically, we will explore the design principles for DNA origami
particles produced by our collaborator Seth Fraden (Brandeis University, USA) to assemble over a given sequence over time, which will allow for an actin-like treadmilling (coordinated polymerization from one end, depolymerization from the other) of a polymer-like structure under e.g., temperature cycling. Such mechanisms could be key in controlling the motor action of prospective molecular machines.
In a second stage (e.g., during a PhD), the intern may develop simulations tools to optimize particle shapes for self-assembly of printed particles produced at PMMH in collaboration with Julien Heuvingh and Olivia du Roure. The successful applicant will have a taste for numerical simulations and working with experimentalists.


LPTMS Internship Proposal: Localization in open quantum systems

Contacts: Alberto Rosso (LPTMS) and Laura Foini (IphT)

Understanding how a many-body quantum system thermalises and when, at the opposite, it keeps memory of the initial preparation is an extraordinary challenge which has attracted enormous attention.
Nowadays, most of the efforts focus on closed systems where the competition between disorder and interactions leads either to thermalization or many body localisation (MBL). In this context the presence of an external bath is believed to induce always thermalisation and destroy any fingerprint of localisation. This is in general not true. The goal of this project (an internship that can lead to a thesis) is to study localisation effects in open systems (e.g. in interaction with a thermal bath and eventually a drive). Two directions will be investigated:
▪ The quench of a many-body system prepared in a state out-of equilibrium and let evolve in a bath of harmonic oscillators
▪ The stationary state of a system in contact with a thermal bath and driven out of equilibrium by irradiation.
In the first case we will focus on non-perturbative effects induced by the strong coupling with the bath.
In the second example we are interested in the nature of the stationary state using a weak coupling Lindblad approach. The work is both numerical and analytical and has strong connections with NMR experiments.

LPTMS Internship Proposal: Searching for topological physics in dissipative Ytterbium gases

Dissipation is ubiquitous in experiments on quantum matter and it typically reduces the timescales
over which pristine quantum phenomena can be investigated or lowers the quality of the
measurements. It’s an “enemy” that has to be fought harshly and roughly. In this internship we
will change the paradigm and consider dissipation as a resource. Dissipation can induce genuine
and interesting quantum effects (see for instance Ref. 1) and we are interesting in proposing
realistic experiments that can reveal them.

We will focus on the experiments on ultracold ytterbium gases that are currently realized in
several laboratories around the world, among which those at Collège de France in Paris (see
Ref. 2). The goal of this internship is to characterize theoretically the interplay between (i) the
dissipative mechanisms that distinguish these atoms and (ii) the unavoidable presence of atomatom
interactions (Ref. 3 presents some first data obtained in Hamburg, Germany). We will
inspect whether the dissipation-induced topological properties presented in the model of
reference 4, where interactions are neglected, can be observed in Ytterbium gases, where
interactions cannot be neglected. The main investigation tool will be advanced numerical
algorithms based on matrix-product states, that allow for the study of dissipative many-body
systems (see Ref. 5 for an article where such methods have been used to characterize dissipative
topological models).

1. F. Verstraete, M. W. Wolf and J. I. Cirac, Nature Physics 5, 633 (2009).
2. R Bouganne et al., New J. Phys. 19, 113006 (2017).
3. K. Sponselee et al., arXiv:1805.11853 (2018).
4. M. S. Rudner and L. S. Levitov, Phys. Rev. Lett. 102, 065703 (2009).
5. F. Iemini, D. Rossini, R. Fazio, S. Diehl and L. Mazza, Phys. Rev. B 93, 115113 (2016)

Leonardo MAZZA