Strongly coupled giant-atom waveguide quantum electrodynamics

TL;DR

The work addresses decoherence and non-Markovian dynamics of superconducting giant atoms coupled to a structured waveguide, going beyond Born–Markov and WW treatments. It develops an exact non-Markovian framework where the dynamics are determined by the spectrum of the composite giant-atom–photonic system, revealing bound states both outside and inside the continuum that govern long-time behavior. A one-to-one correspondence is established between bound-state content (BOCs and BICs) and dynamical outcomes, including finite steady-state excitations and lossless oscillations, enabling decoherence suppression. The results extend to multi-atom configurations and suggest practical routes to entangle distant nodes and realize quantum interconnects, with experimental feasibility in circuit QED and related platforms.

Abstract

Describing systems of superconducting atoms coupled to a continuum of photonic modes at multiple separated locations in a waveguide, waveguide quantum electrodynamics (QED) with giant atoms has emerged as a promising platform for realizing quantum interconnect. Such systems have been reported to exhibit rich phenomena that differ from those of natural atoms. Going beyond the widely used Born-Markov and Wigner-Weisskopf approximations, we investigate the non-Markovian dynamics of one and two giant atoms interacting with a waveguide formed by an array of coupled resonators. We discover that the diverse dynamical behaviors of the giant atoms are intrinsically determined by the energy spectrum of the composite system consisting of the giant atoms and the photonic modes in the waveguide. As long as one and more bound states are present in the energy spectrum, their excited-state probabilities, respectively, tend to stable finite values and lossless Rabi-like oscillations with frequencies proportional to the differences of the bound-state eigenenergies. Our result provides an insightful guideline for suppressing the decoherence of giant atoms and facilitates the development of quantum interconnect devices using giant-atom waveguide QED.

Figures (5)

• Figure 1: Schematic diagram of $N$ giant atoms interacting with a one-dimension nearest-neighbor coupled-resonator array realized in circuit QED system.
• Figure 2: (a) Evolution of the excited-state population $|c(t)|^2$, (b) energy spectrum, and (c) steady-state solution $|c(\infty)|^2$ in different $g_0$ when $\Delta=-0.6h$ and $d=1$. (d) Energy spectrum, (e) steady-state solution $|c(\infty)|^2$, and (f) evolution of $|c(t)|^2$ in different $\Delta$ when $g_0=0.8h$ and $d=3$. (g) Energy spectrum, (h) steady-state solution $|c(\infty)|^2$, and (i) evolution of $|c(t)|^2$ in different $\Delta$ when $g_0=0.8h$ and $d=2$. In (c), (e) and (h), the dots are obtained from numerically solving Eq. \ref{['intfgr']}, the solid lines are from the analytical solution in Eq. \ref{['stdfm']}, and the orange dots cover the values during its persistent oscillation. The red dot in (d) and (g) denotes the energy of BIC. The black solid lines in (f) and (i) are from Eq. \ref{['wwapr']}. We use $L=800$.
• Figure 3: Evolution of $|c(t)|^2$ and energy spectrum for (a) even and (b) odd $d$. We use $\Delta=0$ and other parameter values same as Fig. \ref{['fig2']}(g).
• Figure 4: Energy spectra and evolutions of the concurrence $C(t)$ in different (a) $g_0$ when $\Delta=0.16h$, $d=3$, and $z=1$ and (b) when $\Delta=1.04h$, $d=2$, and $z=1$ and (c) in different $z$ when $\Delta=0.36h$, $g_0=0.6h$, and $d=3$. The type-I BOCs are denoted by orange dots. The type-II BOCs are denoted by green dots. The BICs are denoted by red dots. The analytical results are plotted as the red dashed line.
• Figure 5: (a) Energy spectrum and evolutions of (b) $|c_1(t)|^2$, (c) $|c_2(t)|^2$ and (d) $C(t)$ in different $\Delta$ when $g_0=0.6h$, $d=3$, and $z=3$. The type-I BOCs are denoted by orange dots. The type-II BOCs are denoted by green dots. The BICs are denoted by red dots.