Non-equilibrium dynamics of one-dimensional Bose gases

Tim Langen (Colorado)

I will present a series of experiments with ultracold one-dimensional Bose gases, which are prepared, manipulated and probed using an atom chip. This provides a versatile setting to study many-body physics and, in particular, fundamental questions about equilibration and thermalization in the quantum world.

In the experiments a single gas is coherently split into two parts. This creates a well-defined non-equilibrium situation that can be probed in great detail using matter-wave interferometry. The subsequent dynamics reveal the emergence of a prethermalized steady state, which differs strongly from thermal equilibrium [1,2]. Such thermal-like states had previously been predicted for a large variety of systems, but never been observed directly. A further detailed study of the relaxation process shows that the thermal correlations of the prethermalized state emerge locally in their final form and propagate through the system in a light-cone-like evolution [3]. This provides first experimental evidence for the local relaxation conjecture, which links relaxation processes in quantum many-body systems to the propagation of correlations. Moreover, engineering the initial state of the evolution enables the first direct observation of a generalized thermodynamical ensemble [4]. This points to a natural emergence of classical statistical properties from the microscopic unitary quantum evolution, and forms a cornerstone for a universal framework of non-equilibrium physics. Finally, I will discuss recent advances in the tomography of quantum many-body states [5] and the probing of more complex field theories [6].

[1] M. Gring et al., Science 337, 1318 (2012)
[2] M. Kuhnert et al., Phys. Rev. Lett. 110, 090405 (2013)
[3] T. Langen et al., Nature Physics 9, 640 (2013)
[4] T. Langen et al., Science 348, 207 (2015)
[5] A. Steffens et al., Nature Comm. 6, 7663 (2015)
[6] T. Schweigler et al., arxiv:1505.03126