Photonic Reservoir Engineering via 2D $Λ$-Type Atomic Arrays in Waveguide QED

TL;DR

The paper addresses limitations of conventional EIT in Λ-type wQED by engineering two-dimensional atomic lattices near a photonic crystal waveguide to create structured photonic reservoirs. The Zigzag geometry flattens and broadens the EIT window for robust quantum memory, while the Orthogonal geometry creates multiple transmission resonances that dramatically enhance four-wave mixing with phase-stable, localized nonlinear modes. Key findings include near-rectangular EIT profiles with spectrally isolated absorption bands and highly localized inelastic scattering, yielding memory with higher fidelity and nonlinear optical processes with strong, spectrally selective coupling. This approach provides a pathway toward scalable, integrated quantum photonic devices with programmable light–matter interactions and controlled nonlinear dynamics.

Abstract

Electromagnetically induced transparency (EIT) in $Λ$-type atomic systems underpins quantum technologies such as high-fidelity memory and nonlinear optics, but conventional setups face intrinsic limitations. Standard geometries of one-dimensional atomic chains coupled to waveguides allow only a single bright superradiant channel, while subradiant modes remain weakly accessible, limiting control over collective radiative behavior and dark-state pathways. This leads to unwanted inelastic processes, degrading memory fidelity and reducing nonlinear photon generation efficiency. Here, we propose two two-dimensional (2D) atomic lattice geometries coupled to a photonic crystal waveguide, namely Zigzag and Orthogonal structures. In the Zigzag model, engineered collective super- and subradiant modes produce a flattened EIT window, broadening the transmission bandwidth and suppressing unwanted scattering to enhance quantum memory fidelity. In the Orthogonal model, four-wave mixing (FWM) intensity is amplified by up to six orders of magnitude relative to a conventional one-dimensional $Λ$-type EIT chain with identical $Γ_{1D}$, $Ω_c$, and probe intensity, with localized idler photons forming well-defined spectral modes. These results demonstrate a versatile route to engineer structured photonic reservoirs for on-demand photon generation, high-fidelity quantum storage, and enhanced nonlinear optical processes.

Figures (9)

• Figure 1: Zigzag model: Schematic of an atomic chain of ensembles coupled to a photonic crystal waveguide, forming a multi-photonic structured reservoir for quantum-memory applications.
• Figure 2: Orthogonal model: Schematic of an atomic chain of ensembles coupled to a photonic crystal waveguide, forming a multi-photonic structured reservoir for nonlinear light--matter interactions.
• Figure 3: One-photon transmission spectra of $\Lambda$-type atomic schemes as a function of the probe detuning $\Delta\omega$. The black solid line corresponds to the conventional EIT model, while the green and orange dashed lines represent the Zigzag models with $M=3$ and $M=5$, respectively. The simulation parameters: $\Gamma_{1D} = \Gamma$, $\Gamma_e = 0.1\Gamma$, $\Omega_c = 2\Gamma$, $J_1 = 0.2\Gamma$, $J_2 = 1.6\Gamma$, $\Delta_c = 0$, $k_0 d = \pi/2$, and $a = d$. (a), Engineered EIT-band profile for quantum memory, where $W$ denotes the bandwidth of the EIT transparency window and $W'$ indicates the bandwidth of the adjacent absorption band.
• Figure 4: Inelastic scattering spectra for two incident photons as a function of probe detuning $\Delta\omega$. Panels (a)–(c): conventional EIT model; (d)–(f): Zigzag model. Two-photon inputs with detunings $\Delta\omega = 0$ [(a), (d)], $0.5\Gamma$ [(b), (e)], and $\Gamma$ [(c), (f)]. The simulation parameters: $\Gamma_{1D} = \Gamma$, $\Gamma_e = 0.1\Gamma$, $\Omega_c = 2\Gamma$, $J_1 = 0.2\Gamma$, $J_2 = 1.6\Gamma$, $\Delta_c = 0$, $k_0 d = \pi/2$, and $a = d$.
• Figure 5: One-photon transmission spectra of $\Lambda$-type atomic schemes as a function of the probe detuning $\Delta\omega$. The black solid line corresponds to the conventional EIT model, while the green and orange dashed lines represent the Orthogonal models with two atoms per unit cell $N = 2$, and with $M=10$ and $M=20$, respectively. The simulation parameters are $\Gamma_{1D} = \Gamma$, $\Gamma_e = 0.1\Gamma$, $\Omega_c = 2\Gamma$, $J_1 = 3\Gamma$, $J_2 = 6\Gamma$, $\Delta_c = 0$, $k_0 d = \pi/2$, and $a = d$. (a) Engineered transmission profile for the four-wave mixing (FWM) response, where $W_1$ and $W_3$ denote the bandwidths of the additional and main EIT transparency windows, respectively, and $W_2$ corresponds to the absorption band separating these two transparency windows.