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Chinese Physics B

Oscillating bound states in waveguide QED systems with two giant atoms

Liangbin He, T J Li, Zhen Yi, Lihui Sun, Wenju Gu

Published Jun 22, 2026• 0 citations
Publisher

Abstract

Abstract We investigate the dynamics of two two-level giant atoms coupled to a one-dimensional waveguide in separate and braided configurations. Using the resolvent method, the quantum dynamics are determined by the poles of the Green’s function. We identify conditions under which three real poles with distinct eigenfrequencies emerge, corresponding to three bound states in the continuum (BICs). Their superposition gives rise to oscillating BICs. In this regime, the atomic excitation oscillates between the two atoms, while the photon field remains confined between the coupling points and exhibits persistent oscillations. The maxima of the photon field distribution coincide with those of the atomic excitations, reflecting the atom-photon bound-state nature. The revival of the photon distribution reveals the coherent interaction between the two giant atoms mediated by the BICs. This work broadens the fields of quantum information storage and manipulation by leveraging larger Hilbert spaces enabled by multiple nonradiative BICs.

DOI
10.1088/1674-1056/ae7ffa

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Abstract We investigate the dynamics of two two-level giant atoms coupled to a one-dimensional waveguide in separate and braided configurations. Using the resolvent method, the quantum dynamics are determined by the poles of the Green’s function. We identify conditions under which three real poles with distinct eigenfrequencies emerge, corresponding to three bound states in the continuum (BICs). Their superposition gives rise to oscillating BICs. In this regime, the atomic excitation oscillates between the two atoms, while the photon field remains confined between the coupling points and exhibits persistent oscillations. The maxima of the photon field distribution coincide with those of the atomic excitations, reflecting the atom-photon bound-state nature. The revival of the photon distribution reveals the coherent interaction between the two giant atoms mediated by the BICs. This work broadens the fields of quantum information storage and manipulation by leveraging larger Hilbert spaces enabled by multiple nonradiative BICs.
We study the bound states in the continuum (BIC) in a system of two identical two-level giant atoms coupled to a one-dimensional waveguide. By deriving general dark-state conditions, we clarify how coupling configurations and atomic parameters influence decay suppression. Through analysis of the long-time dynamical behaviors of atoms and bound photons, we carry out a detailed classification of bound states and explore the connections between these dynamical behaviors and the system's intrinsic light-matter interactions. The system supports static bound states with persistent atomic excitations, and oscillating bound states with periodic atom-photon or atom-atom excitation exchange. Under certain conditions, oscillating bound states can contain more harmonic components owing to the emergence of additional quasi-dark modes, rendering them promising platforms for high-capacity quantum information processing. These findings advance the understanding of BIC in waveguide quantum electrodynamics with multiple giant atoms and reveal their prospective applications in quantum technologies.
Abstract We investigate phase-controlled bound states in a one-dimensional photonic waveguide coupled to an artificial giant atom at two distant sites. Specifically, we identify the bound state out of the continuum (BOC) and the bound state in the continuum (BIC) and derive the exact existence condition for the BOC. Furthermore, we analytically determine the BIC’s frequency and photonic distribution profile. Remarkably, our analysis reveals quantum beats in both atomic and photonic dynamics, arising from coherent oscillations between the BIC and BOC. These results establish a novel approach for manipulating waveguide quantum electrodynamics via engineered bound states, with potential applications in quantum information processing.
We study the dynamics of two giant atoms interacting with a coupled resonator waveguide (CRW) beyond the Markovian approximation. The distinct atomic configurations determine the number of bound states in the continuum (BICs), leading to different dynamical behaviors. Our results show that when the system supports two BICs, Rabi oscillations dominate the dynamics, whereas fractional population dynamics emerge in the presence of a single BIC. The connection between these dynamics and the existence of BICs is further verified by analyzing the photonic distribution in the CRW during time evolution. These findings challenge the conventional notion that the environment always induces dissipation and decoherence. Instead, the bound states in the CRW-emitter coupled system can suppress complete dissipation of the emitters. We also quantitatively illustrate the memory effect of the waveguide, which serves as the environment of the giant-atom feature that can only be captured within our non-Markovian treatment. This work offers an effective approach for controlling dissipative dynamics in open quantum systems.
We find the phase-controlled bound state out of the continuum~(BOC) and bound state in the continuum~(BIC) in an artificial giant atom dressed one-dimensional photonic waveguide where the giant atom couples to the waveguide via two distant sites. We obtain the existence condition of the BOC as well as the frequency and the photonic distribution in the BIC. More interestingly, we predict the quantum beats in the atomic and photonic dynamical evolution, which is induced by the oscillation between the BIC and the BOCs. These findings provide an approach to manipulate the waveguide system via the bound states.
Giant atoms, which couple to a waveguide through multiple spatially separated connection points beyond the dipole approximation, provide a versatile route for quantum information processing based on interference-induced bound states in the continuum (BICs). While multi-giant-atom architectures are being developed toward giant-atom quantum networks, the role of direct coupling between the giant atoms, in particular the associated coupling phase, in atomic dynamics remains insufficiently understood. Here we take a first step toward addressing this issue by studying a two-giant-atom waveguide-QED model. We show that the coupling phase can be used to control both the number of BICs and their profiles for both of photon and atoms. More interestingly, the presence of BICs gives rise to a variety of dynamical behaviors, providing an effective mechanism for tailoring quantum-state evolution in giant-atom waveguide-QED systems. Our results highlight coupling-phase engineering as a useful tool for controlling interference, bound states, and quantum dynamics in nonlocal light--matter interfaces.
It is known that the superposition of two bound states in the continuum (BICs) leads to the phenomenon of an oscillating bound state, where excitations mediated by the continuum modes oscillate persistently. We perform exact calculations for the oscillating BICs in a one-dimensional photonic lattice coupled to a ``giant atom'' at multiple points. Our work is significantly distinct from previous proposals of oscillating BICs in continuous waveguide systems due to the presence of a finite energy band contributing band-edge effects. In particular, we show that the bound states outside the energy band are detrimental to the oscillating BIC phenomenon, and can be suppressed by increasing either the number of coupling points or the separation between each coupling point. Crucially, non-Markovianity is necessary for the existence of oscillating BICs, and the oscillation amplitude increases with the characteristic delay time of the giant atom interactions. We also propose an initialization scheme in the BIC subspace. Our work be experimentally implemented on current photonic waveguide array platforms and opens up prospects in utilizing reservoir engineering for the storage of quantum information in photonic lattices.