In a collaboration with Enrique Rico and Enrique Solano (Department of Physical Chemistry, University of the Basque Country), Martin Weitz recently published the work of his group on quantum Rabi dynamics of trapped ions.
The coupling of a two-level system with an electromagnetic field, whose fully quantized version is the quantum Rabi model, is among the central topics of quantum physics. When the coupling strength becomes large enough that the field mode frequency is reached, the deep strong coupling regime is approached, and excitations can be created from the vacuum. Here the authors demonstrate a periodic variant of the quantum Rabi model in which the two-level system is encoded in the Bloch band structure of cold rubidium atoms in optical potentials. With this method they achieve a Rabi coupling strength of 6.5 times the field mode frequency, which is far in the deep strong coupling regime, and observe a subcycle timescale raise in bosonic field mode excitations. In a measurement recorded in the basis of the coupling term of the quantum Rabi Hamiltonian, a freezing of dynamics is revealed for small frequency splittings of the two-level system, as expected when the coupling term dominates over all other energy scales, and a revival for larger splittings. The work demonstrates a route to realize quantum-engineering applications in yet unexplored parameter regimes.
Examples of obtained image data: (a) Series of real space images for the system initially prepared in the qubit excited state of the quantum Rabi Hamiltonian, with ωq2π=2380(40)Hz and gω=6.5(5), after deconvolution of the obtained raw absorption imaging data of the atomic ensemble accounting for the point spread function of the used optics. From left to right the interaction time increases in steps of 50 μs. Despite the limited instrumental optical resolution, a splitting up of the atomic cloud is observed. b Series of time-of-flight images of the atomic cloud, for the same system state as in a. The numbers on the left-hand side represent the measured atomic momentum p, while the on the right-hand side the corresponding quasimomentum q is given. [Source: Nature, figure 5 of the publication]
Publication: Quantum Rabi dynamics of trapped atoms far in the deep strong coupling regime, Nature Communications 14, 954 (2023)
https://www.nature.com/articles/s41467-023-36611-z#Ack1