Description of the thesis topic

Superfluidity is the remarkable collective behavior of quantum fluids characterized by vanishing viscosity and frictionless flow. It manifests through features such as persistent currents, quantized vortices, and critical velocities for flow stability. In low-dimensional systems—particularly in one dimension (1D)—quantum fluctuations play an enhanced role, leading to profound differences compared to higher dimensions. For example, theoretical work predicts the presence of a non-zero friction force at any flow velocity, driven solely by quantum fluctuations [1,2]. The competition between this quantum friction and the quasi-long-range order that emerges in 1D at low temperatures challenges the conventional definition of superfluidity.

Optical ring traps provide strong transverse confinement and support rotating persistent currents [3], making them ideal platforms to investigate superfluidity. However, achieving the strongly interacting 1D regime is technically demanding; so far, experiments have only reached mean-field or marginally 1D conditions. The first objective of this project is therefore to design and implement optical traps capable of confining Bose–Einstein condensates (BECs) in tightly focused ring-shaped potentials (see Fig. 1). These traps will be created by shaping the transverse phase profile of laser beams using spatial light modulators—programmable phase masks that imprint arbitrary phase and/or intensity profiles onto the beams. Combined with additional optical lattice beams that provide longitudinal confinement, this setup will enable access to the strongly correlated 1D regime.

The 1D ring traps developed in this project will then be used to study exotic superfluid behavior in reduced dimensionality. They will allow for the characterization of superfluid critical velocities, the dynamics of excitations, and the role of quantum coherence. Using tunable interactions in potassium BECs, the project will explore these effects across a broad range of regimes, from mean-field to strongly correlated. In the longer term, these advances will enable exploration of the fate of 1D superfluidity beyond the mean-field framework, provide experimental validation of analytical predictions, and guide the development of future theoretical approaches.

Keywords: Ultracold quantum gases, superfluidity, quantum simulations

[1] RMP 94, 041001 (2022) - Atomtronic circuits: From many-body physics to quantum technologies
[2] PRA 85, 053627(2012) - Probing superfluidity of a mesoscopic Tonks-Girardeau gas
[3] PRA 91, 063619 (2015) - Dynamic structure factor and drag force in a one-dimensional strongly interacting Bose gas at finite temperature

Work Context

Integration: The PhD will be hosted at the PhLAM laboratory (University of Lille, CNRS) within the Quantum Systems team, which includes seven permanent researchers, five PhD students, and one postdoctoral fellow. The selected candidate will contribute to experiments based on an existing potassium BEC platform and will benefit from strong local theoretical support as well as collaborations with theory and experimental groups in Nice and Paris.

Constraints and risks

Requirements:
- Master's degree (M2) or equivalent (5 years of university education)
- Knowledge of quantum mechanics and atomic physics
- Preferably some experience in an experimental laboratory

Additional Information

Financement : La thèse est entièrement financée par un projet en cours de l'Agence Nationale de la Recherche (ANR) et par le programme ULille GRAEL.