Conference

The advent of ultracold molecules opens the possibility to explore chemical reactions with perfect control of the quantum states of the reactants. We report on several surprising results of our work with ultracold NaLi molecules. First, we demonstrate a factor of 100 control of reaction rates between NaLi molecules and Na atoms by changing the atom's spin state. This ability to slow reactions allowed us to demonstrate sympathetic cooling of molecules for the first time. Next, we explore two very different collisional resonances. A resonance in NaLi+Na reactions exemplifies the standard description of chemical resonances. The other, for NaLi+NaLi, is the first ultracold molecule-molecule resonance observed and runs completely counter to the standard description. Simple models relate the complex chemical dynamics to the simple physics of a Fabry-Perot resonantor and point a number of open questions in chemical dynamics that can be explored with ultracold molecules.

Turbulent radiation flow is ubiquitous in many physical systems where light–matter interaction becomes relevant. Photon bubble instabilities, in particular, have been identified as a possible source of turbulent radiation transport in astrophysical objects such as massive stars and black hole accretion disks. Here, we report on the experimental observation of a photon bubble instability in cold atomic gases, in the presence of multiple scattering of light. A two-fluid theory is developed to model the coupled atom–photon gas and to describe both the saturation of the instability in the regime of quasi-static bubbles and the low-frequency turbulent phase associated with the growth and collapse of photon bubbles inside the atomic sample. We also employ statistical dimensionality reduction techniques to describe the low-dimensional nature of the turbulent regime. The experimental results reported here, along with the theoretical model we have developed, may shed light on analogue photon bubble instabilities in astrophysical scenarios. Our findings are consistent with recent analyses based on spatially resolved pump–probe measurements.

"S. Tiwari, S. Rammohan, A. Mishra, A. Pendse, A. K. Chauhan, R. Nath, F. Engel, M. Wagner, R.Schmidt, F. Meinert, A. Eisfeld and S. Wüster Indian Institute of Science Education and Research, Bhopal India Palacký University, Olomouc, Czech Republic Indian Institute of Science Education and Research, Pune, India Max Planck Institute for the Physics of Complex Systems, Dresden, Germany Universität Stuttgart, Germany Max-Planck-Institute of Quantum Optics and MCQST, Garching, Germany Rydberg Atoms in highly excited electronic states with n=30-200 can be excited within BoseEinstein condensates (BECs), and while lifetimes are shorter than in vacuum [1,2], they live long enough to cause a response of the BEC mean field [3]. During this, thousands of ground-state atoms are present within the Rydberg orbit, allowing the study of atoms moving within atoms [4]. We present beyond-mean field models of the joint Rydberg-BEC dynamics, showing how either can be used to probe the other. For multiple Rydberg atoms in a single electronic state, we show that the phase coherence of thecondensate allows the tracking of mobile Rydberg impurities akin to the function of bubblechambers in particle physics [5]. For a single Rydberg atom with multiple electronic states, weprovide spectral densities of the BEC as a decohering environment [6], and show that the BECcan image a signature of the entangling evolution that causes Rydberg q-bit decoherence [7] or serve as non-Markovian environment for quantum simulations. [1] Schlagmüller et al. PRX 6 (2016) 031020. [2] Kanungo et al. PRA 102 (2020) 063317. [3] Balewski et al. Nature 502 (2013) 664. [4] Tiwari et al. arXiv:2111.05031 (2021) [5] Tiwari et al. PRA 99 (2019) 043616. [6] Rammohan et al. PRA 103 (2021) 063307. [7] Rammohan et al. PRA(Letters) 104 (2021) L060202."