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Physical Review A

Coherent control of spontaneous emission for a giant driven Λ -type three-level atom

Ya Jun Yang, Ge Sun, Jing Li, Jing Lu, Lan Zhou

Published Jan 7, 2025• 11 citations
Publisher

Abstract

Quantum optics with giant atoms provides a new approach for implementing optical memory devices at the atomic scale. Here, we theoretically investigate the relaxation dynamics of a single driven three-level atom interacting with a one-dimensional waveguide via two coupling points. Under certain conditions, after long-time dynamics, we find that the population of the giant atom can either remain stable or exhibit regular periodic oscillations, while photons are trapped within the region of the giant atom. This phenomenon cannot be realized using a two-level atom configured with two coupling points. It is noteworthy that the atomic excitation probability of a stable bound state is a constant value, which is determined by the size of the atom. Importantly, the size of the atom, defined as the distance between the two coupling points, is significantly larger than the wavelength of the light field, which is a necessary condition for the existence of oscillating bound states.

DOI
10.1103/physreva.111.013707

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Quantum optics with giant atoms provides a new approach for implementing optical memory devices at the atomic scale. Here, we theoretically investigate the relaxation dynamics of a single driven three-level atom interacting with a one-dimensional waveguide via two coupling points. Under certain conditions, after long-time dynamics, we find that the population of the giant atom can either remain stable or exhibit regular periodic oscillations, while photons are trapped within the region of the giant atom. This phenomenon cannot be realized using a two-level atom configured with two coupling points. It is noteworthy that the atomic excitation probability of a stable bound state is a constant value, which is determined by the size of the atom. Importantly, the size of the atom, defined as the distance between the two coupling points, is significantly larger than the wavelength of the light field, which is a necessary condition for the existence of oscillating bound states.
Coherent Control of Spontaneous Emission for a giant driven ΛΛΛ-type three-level atom
Quantum optics with giant atoms provides a new approach for implementing optical memory devices at the atomic scale. Here, we theoretically study the relaxation dynamics of a single driven three-level atom interacting with a one-dimensional waveguide, via two coupling points. Under certain conditions, after the long-time dynamics, we found that the population of giant atom can either maintain stable values or exhibit regular periodic oscillation behavior, while photons can be trapped in the region of giant atoms. This phenomenon is not achievable using a two-level atom with two legs. It is worth noting that the atomic excitation probability of a stable bound state is a constant value, which is determined by the size of the atom. Crucially, the size of the atom (the distance between the two coupling points) is much larger than the wavelength of the light field, which is a necessary condition for the existence of oscillating bound states.
The non-Markovian effects of open quantum systems subjected to external environments are deemed to be valuable resources in quantum optics and quantum information processing. In this work, we construct the model Hamiltonian of three-level giant atom with multiple coupling points in the semi-infinite photonic waveguide via complex coupling coefficients and investigate the non-Markovian dynamics of the three-level giant atom driven by a classical laser field. In the non-Markovian regime, the traveling time of a photon between different coupling points is sufficiently large compared to the inverse of the bare relaxation rate of the giant atom. We derive the analytical expressions for the probability amplitudes of the driven three-level giant atom by solving a set of delay differential equations and obtain two independent conditions of bound states' formation that can inhibit the dissipation. We find two different types of bound states (including the static bound states and the periodic equal-amplitude oscillating bound states) and discuss the physical origins of the bound states' formation. Moreover, we discuss the case of the driven three-level giant atom interacting with the infinite photonic waveguide, where there is only one purely imaginary solution (i.e., only one bound-state condition exists) for its complex frequency (coming from the absence of mirror at one end of the waveguide) compared to that of a driven three-level giant atom coupling with a semi-infinite photonic waveguide. With this, we also find two different types of bound states, including the static bound state and the periodic equal-amplitude oscillating bound states. We study the influences of the phase in the coupling strength on the bound states in semi-infinite and infinite photonic waveguides. The presented protocol might open a way to better understand exactly the non-Markovian dynamics of driven multilevel giant atoms interacting with semi-infinite (or infinite) photonic waveguides.
We investigated the spontaneous emission of a giant atom coupled with a semi-infinite waveguide. Our model considers the giant atom a two-level system coupled to the semi-infinite waveguide at two points. Based on the Hamiltonian in real space, the first-order delay-differential equation for the atomic excitation amplitude is obtained using the Schrödinger equation. Furthermore, the dynamics of spontaneous emission controlled by quantum coherent feedback due to the semi-infinite waveguide in the non-Markov regime are discussed in two cases, with the coupling strengths between the giant atom and the semi-infinite waveguide at the two coupling points being identical in one case and having a phase difference in the other case. The spontaneous emission exhibits partial decay due to multiple excitations from the quantum feedback and two-point coupling. When the coupling strengths are identical, the decay of the atomic excitation can be either increased or inhibited substantially, even forming a steady state, due to the self-interference due to the two-point coupling. The quantum coherent feedback can either further increase the decay of the excited state or maintain the steady state formed by self-interference. Moreover, a new steady state can be built due to quantum coherent feedback, which cannot exist in the self-interference system. The decay rates can also be increased or decreased by manipulating the phase difference between the coupling strengths at the two coupling points. It can destroy the steady state formed by self-interference or build a steady state based on the chosen phase difference. One can leverage quantum coherent feedback to manipulate the steady state value of the population of the excited states by adjusting the phase difference. The dissipation can increase the decay rates of the excited states. Furthermore, it also destroys steady states. Our results may find applications in developing quantum devices such as quantum memory based on giant atom-waveguide systems.
We study the non-Markovian dynamics of a two-level giant atom interacting with a one-dimensional semi-infinite waveguide through multiple coupling points, where a perfect mirror is located at the endpoint of the waveguide. The system enters a non-Markovian process when the travel time of the photon between adjacent coupling points is sufficiently large compared to the inverse of the bare relaxation rate of the giant atom. The photon released by the spontaneous emission of the atom transfers between multiple coupling points through the waveguide or is reabsorbed by the atom with the photon emitted via the atom having completed the round trip after reflection of the mirror, which leads to the photon being trapped and forming bound states. We find that three different types of bound states can be formed in the system, containing the static bound states with no inversion of population, the periodic equal amplitude oscillation with two bound states, and the periodic nonequal amplitude oscillation with three bound states. The physical origins of the three bound states' formation are revealed. Moreover, we consider the influences of the dissipation of unwanted modes and dephasing on the bound states. Finally, we extend the system to a more general case involving many giant atoms coupled into a one-dimensional semi-infinite waveguide. The obtained set of delay differential equations for the giant atoms might open a way to better understand the non-Markovian dynamics of many giant atoms coupled to a semi-infinite waveguide.
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.
Controlling radiative dynamics of a giant ΛΛΛ-type atom via interference induced by the vacuum of a waveguide
We investigate the dynamics of a ΛΛΛ-type giant atom (GA) whose both transition coupled to the guided modes of a one-dimensional (1D) waveguide at two spatially separated points with the GA initially excited and the electromagnetic (EM) modes of waveguide in vacuum. The spontaneous emission properties of this GA is investigated by solving the delay-differential equation for the amplitude of the 3GA in its excited state. Signatures of non-Markovian behavior is manifested in a population trapping in the excited state of the GA in the regime where the distance ddd of the coupling points is smaller or comparable to the coherent length LLL characterizing the width of the emitted wave packet. And an exact Markovian dynamics is also found when d≥Ld\geq Ld≥L via the inference by adjusting the energy spacing and the inherent time delay besides the complex phases in the atom-light coupling, matching the behavior of a small atom coupled to a waveguide.