Quantum Rabi dynamics of trapped atoms far in the deep strong coupling regime

TL;DR

This paper demonstrates a method to achieve deep strong coupling in the quantum Rabi model using cold atoms, revealing new quantum dynamics and potential for quantum engineering applications.

Contribution

The authors realize a deep strong coupling regime in the quantum Rabi model with cold atoms, enabling exploration of previously inaccessible quantum phenomena.

Findings

Achieved a Rabi coupling strength 6.5 times the field mode frequency.

Observed a subcycle timescale increase in bosonic excitations.

Revealed dynamics freezing and revival depending on two-level system splitting.

Abstract

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 we 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 we 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. Our work demonstrates a route to realize quantum-engineering applications in yet unexplored parameter regimes.