Abstract
Light-matter interaction, and the understanding of the fundamental physics behind, is the scenario of emerging quantum technologies. Solid state devices allow the exploration of new regimes where ultrastrong coupling strengths are comparable to subsystem energies, and new exotic phenomena like quantum phase transitions and ground-state entanglement occur. While experiments so far provided only spectroscopic evidence of ultrastrong coupling, we propose a new dynamical protocol for detecting virtual photon pairs in the dressed eigenstates. This is the fingerprint of the violated conservation of the number of excitations, which heralds the symmetry broken by ultrastrong coupling. We show that in flux-based superconducting architectures this photon production channel can be coherently amplified by Stimulated Raman Adiabatic Passage, providing a unique tool for an unambiguous dynamical detection of ultrastrong coupling in present day hardware. This protocol could be a benchmark for control of the dynamics of ultrastrong coupling architectures, in view of applications to quantum information and microwave quantum photonics.
Highlights
Strong coupling between atoms and quantized modes of an electromagnetic cavity[1] provides a fundamental design building block of architectures for quantum technologies[2]
In the ultrastrong coupling (USC) regime g/ωc ∼ 0.1 − 1, the full HR comes into play, leading to spectroscopic signatures (see Fig. 1(a)) as the Bloch-Siegert shift observed in ref.[11], and drastically altering the JC eigenstates which are mixed by USC
Proposals of dynamical detection of USC20,22 aim at the detection of such virtual photons[21] by converting them to real ones
Summary
Strong coupling between atoms and quantized modes of an electromagnetic cavity[1] provides a fundamental design building block of architectures for quantum technologies[2] This regime is achieved when the coupling constant g is large enough to overcome the individual decoherence rates of the mode and of the atom, g κ, γ, and it has been observed in many experimental platforms from standard quantum optical systems[1,3], to architectures of artificial atoms (AA)[4,5,6]. In such systems small cavity volumes and large AA’s dipoles yield values of g up to 1% of the cavity angular frequency ωc and of the AA excitation energy ε This allows to perform the rotating wave approximation (RWA) yielding the Jaynes-Cummings (JC) model of quantum optics[1], which describes the dynamics in terms of individual excitations exchanged between atom and mode. Demonstration of coherent dynamics in the USC regime would be a benchmark for quantum control, with appealing applications ranging from microwave quantum technologies[28,29,30,31,32] to dynamical control of quantum phase transitions[33,34]
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