Chaos from a Chilled Cloud of Atoms
A butterfly beats its wings in one part of the world and stirs up a hurricane in another part. That’s the proverbial way of explaining chaotic behavior, which has been observed in a plethora of classical dynamical systems but only in a few quantum systems and in fewer still quantum systems comprising many particles. Markus Oberthaler from the University of Heidelberg, Germany, and colleagues have now mapped, with exquisite detail, the onset of chaos in a many-particle quantum system driven by a periodic perturbation. Their mapping approach could help researchers get to grips with how chaos emerges in, and affects, many-body quantum systems.
Oberthaler and co-workers began their study by preparing a Bose-Einstein condensate of cold atoms that had two components with different internal spins and then coupling the components with a microwave pulse. The coupling was such that the condensate formed the many-particle quantum equivalent of the anharmonic oscillator, a classical oscillator that can display chaotic behavior if driven by a periodic perturbation of specific frequency and phase. The researchers then drove the system by periodically varying the amplitude of the pulse and thus the strength of the coupling. Next they mapped the phase space spanned by the relative quantum phase of the two components and the relative number of atoms in them using an approach that involved a magnetic field, another microwave pulse, and absorption imaging. And they did the mapping for a range of driving amplitudes. They found a small region of chaotic trajectories in the phase space at a moderate driving amplitude and a large chaotic region at larger amplitude—just like those that characterize the phase space of the anharmonic oscillator undergoing chaotic dynamics.
This research is published in Physical Review A.
–Ana Lopes
Ana Lopes is a Senior Editor of Physics.