Multiphoton Quantum Rabi Oscillations in Ultrastrong Cavity QED

TL;DR

This paper demonstrates that in ultrastrong cavity QED, multiphoton vacuum Rabi oscillations occur, enabling new quantum state manipulations and entangled state generation in circuit-QED systems.

Contribution

It reveals the possibility of multiphoton exchanges in ultrastrong coupling regimes, expanding the understanding of cavity QED beyond single-photon interactions.

Findings

Experimental observation of two- and three-photon Rabi oscillations

Potential for generating Fock states and entangled qubit states

Modification of vacuum Rabi oscillation concept in ultrastrong coupling

Abstract

When an atom is strongly coupled to a cavity, the two systems can exchange a single photon through a coherent Rabi oscillation. This process enables precise quantum-state engineering and manipulation of atoms and photons in a cavity, which play a central role in quantum information and measurement. Recently, a new regime of cavity QED has been reached experimentally where the strength of the interaction between light and artificial atoms (qubits) becomes comparable to the atomic transition frequency or the resonance frequency of the cavity mode. Here we show that this regime can strongly modify the concept of vacuum Rabi oscillations, enabling multiphoton exchanges between the qubit and the resonator. We find that experimental state-of-the-art circuit- QED systems can undergo two- and three-photon vacuum Rabi oscillations. These anomalous Rabi oscillations can be exploited for the realization of efficient Fock-state sources of light and complex entangled states of qubits.