Impact Lab

A versatile platform for atom-light interactions

With this experiment, we explore and manipulate ultracold atoms in diverse self-generated, dynamical optical lattices provided by quantized light fields of several cavity modes. The dispersive coupling between cavity modes and quantum gases gives rise to photon-mediated interactions that can cause transitions to new quantum phases. Their static and dynamic properties can be investigated in real time in non-destructive ways by the light fields leaking from the cavities. This finite decay rate not only constitutes a powerful observable, but also alows to investigate the effect of dissipation in open systems onto quantum phases.

The experiment is designed in a modular way, that allows for rapid exchange of the cavity system. This enables us to explore a variety of different systems. Currently, a platform with two optical high-finesse cavities that cross under an angle of 60° is loaded into the vacuum chamber.

27 Feb 2019

Two-mode Dicke model from non-degenerate polarization modes

We realize a two-mode Dicke model by coupling a BEC to the two fundamental polarization modes of a single cavity, to which we couple via both the scalar and vectorial polarizabilities of the atoms. By independently tuning the relative interaction strengths, we determine the effect on the self-organization phase transition, demonstrating a crossover from a single-mode to a two-mode Dicke model.

17 Nov 2017

Coupling two order parameters in a quantum gas

We use a quantum gas to engineer an adjustable interaction at the microscopic level between two orders, and demonstrate scenarios of competition, coexistence and coupling between them. In the latter case, intriguingly, the presence of one order lowers the critical point of the other. We characterize the intertwining between these orders by measuring the composite order parameter and the elementary excitations. We explain our results with a mean-field free energy model, which is derived from a microscopic Hamiltonian.

19 Apr 2017

Monitoring and manipulating Higgs and Goldstone modes

We study the Higgs and Goldstone modes in a supersolid quantum gas that is created by coupling a Bose-Einstein condensate symmetrically to two optical cavities. The cavity fields form a U(1)-symmetric order parameter that can be modulated and monitored along both quadratures in real time. This enables us to measure the excitation energies across the superfluid-supersolid phase transition, establish their amplitude and phase nature, as well as characterize their dynamics from an impulse response. Furthermore, we can give a tunable mass to the Goldstone mode at the crossover between continuous and discrete symmetry by changing the coupling of the quantum gas with either cavity. 

28 Sep 2016

Supersolid formation in a quantum gas

We report on the crystallization of a superfluid quantum gas to a supersolid by breaking continuous translational symmetry. The control over the coupling strength between the atomic cloud and two optical cavities allows us to tailor the cavity-mediated interactions between the atoms in such a way, that they give rise to a structural phase transition. The continuous symmetry breaking finds its origin at the interplay of two discrete symmetries associated with a self-organisation phase transition to each cavity. We use the light fields leaking from the cavities to monitor the position of the crystalline structure in real time, and to directly detect the ground state degeneracy of the supersolid.

9 Jun 2014

Tunable lens setup for transporting ultracold atoms

We implemeted an optical setup with focus-tunable lenses to dynamically control the waist and focus position of a laser beam, in which we transport a trapped ultracold cloud of 87Rb over a distance of 28 cm from our MOT chamber to the science chambe. The scheme allows us to shift the focus position at constant waist, providing uniform trapping conditions over the full transport length. Furtheron, with the chosen configuration we can dynamically change the waist size at fixed focus position.