Ultrastrong waveguide QED with giant atoms

Abstract

Quantum optics with giant emitters has shown a new route for the observation and manipulation of non-Markovian properties in waveguide-QED. In this paper we extend the theory of giant atoms, hitherto restricted to the perturbative light-matter regime, to deal with the ultrastrong coupling regime. Using static and dynamical polaron methods we address the low energy subspace of a giant atom coupled to an Ohmic waveguide beyond the standard rotating wave approximation. We analyze the equilibrium properties of the system by computing the atomic frequency renormalization as a function of the coupling characterizing the localization-delocalization quantum phase transition for a giant atom. We show that virtual photons dressing the ground state are non-exponentially localized around the contact points but decay as a power-law. Dynamics of an initially excited giant atom are studied, pointing out the effects of ultrastrong coupling on the Lamb shift and the spontaneous emission decay rate. Finally we comment on the existence of the so-called oscillating bound states beyond the rotating wave approximation.

Virtual Excitations and Entanglement Dynamics and Polygamy in Three Ultra‐Strongly Coupled Systems

“…Ultra strong coupling (USC) physics, in which the coupling becomes comparable to the system's frequencies, has emerged as a new and increasingly popular domain. [1][2][3][4][5][6][7] The importance of the USC lies in its potential effects on several physical phenomena, including photon blockade, [8] Purcell effect, [9] Zeno effect, [10] and maintaining entanglement by virtual excitations of a vacuum state. [11,12] The fluctuations of the vacuum are one of the most striking phenomena of modern physics and have colossal applications in quantum technologies.…”

“…As a result, the rotating wave approximation (RWA), where CRT is neglected, breaks down. [2,7,17] Multipartite systems made of coupled oscillators are central in physics [18][19][20] and for reviews we cite the references. [21][22][23] In fact, they lead to the modeling of coupled ions in ion traps, [24] arrayed coupled nano-sized electromechanical devices, [25] light propagation in inhomogeneous media, [26] and a nitrogen vacancy ensemble embedded in a diamond nanobeam.…”

Dynamics Near a Photonic Band-Edge: Strong Coupling Effects Beyond Rotating-Wave Approximation

“…Much of these investigations, however, have focused on the weak light-matter coupling regime, where the Rotating-Wave Approximation (RWA), a conventional approximation in quantum optics, is valid. In the regime of strong or ultrastrong light-matter coupling [19,20] this approximation can break down and novel phenomena are expected to emerge [21][22][23][24][25]: in this work we focus on such regimes.…”