Amplifying Decoherence-Free Many-Body Interactions with Giant Atoms Coupled to Parametric Waveguide

TL;DR

The paper tackles squeezing-induced decoherence that hinders scalable quantum interactions by proposing a traveling-wave parametric amplifier coupled to nonlocal, multi-point giant atoms. Through destructive interference across at least three coupling points, the setup achieves decoherence-free exchange ($J_c$) and pairing ($J_p$) interactions that are tunable via parametric gain and pump-phase, while suppressing noise. The authors derive explicit expressions for $J_p$ and $J_c$, map the system to the anisotropic XY model via Jordan-Wigner, and identify quantum-critical behavior that can be probed with fidelity susceptibility, all within a scalable superconducting-circuit platform using a JTWPA. The approach eliminates next-nearest-neighbor couplings and offers a robust, programmable route to simulating strongly correlated many-body physics with noise resilience in waveguide QED. This work showcases a versatile pathway toward scalable quantum simulation and control in hybrid photonic-atom networks.

Abstract

Parametric amplification offers a powerful means to enhance quantum interactions through field squeezing, yet it typically introduces additional noise which accelerates quantum decoherence, a major obstacle for scalable quantum information processing. The squeezing field is implemented in cavities rather than continuous waveguides, thereby limiting its scalability for applications in quantum simulation. Giant atoms, which couple to waveguides at multiple points, provide a promising route to mitigate dissipation via engineered interference, enabling decoherence-free interactions. We extend the squeezing-amplified interaction to a novel quantum platform combining giant atoms with traveling-wave parametric waveguides based on $χ^{(2)}$ nonlinearity. By exploiting destructive interference between different coupling points, the interaction between giant atoms is not only significantly enhanced but also becomes immune to squeezed noise. Unlike conventional waveguide quantum electrodynamics without a squeezing pump, the giant emitters exhibit both exchange and pairing interactions, making this platform particularly suitable for simulating many-body quantum physics. More intriguingly, the strengths of these interactions can be smoothly tuned by adjusting the squeezing and coupling parameters. Our architecture thus provides a versatile and scalable platform for quantum simulation of strongly correlated physics and paves the way toward robust quantum control in many-body regimes.

Figures (8)

• Figure 1: (a) Scheme of two giant atoms coupled to a nonlinear traveling-wave parametric waveguide of length $L$, pumped by counter-propagating fields at $2\omega_0$ to generate bidirectional squeezed vacuum fields, with pump phases $\overset{\rightarrow}{\theta}$ and $\overset{\leftarrow}{\theta}$. Blue dotted arrow denotes the coherent-exchange interaction $J_c$. The red dashed arrow represents the pairing interaction $J_p$. (b) Scheme of a pair of giant atoms coupled to the waveguide at three equidistant points by distance $\pi$. And the phase difference is $k_0\varphi_1$, with $\varphi_1+\varphi_2=\pi$.
• Figure 2: Dependence of pairing and exchange interaction strengths on (a) parametric gain $\mathcal{G}$, with fixed phase difference $\theta_- = 0$ and atomic spacing $d_s = 0.2\pi$; and (b) phase difference $\theta_-$, with fixed parametric gain $\mathcal{G} = 0.8$ and atomic spacing $d_s = 0.2\pi$. (c) The ratio $J_p/J_c$ as a function of atomic spacing $d_s$, with parametric gain $\mathcal{G} = 0.8$ and phase difference $\theta_- = 0$. The black dots indicate $J_p=0$. The vertical dashed line marks $J_c=0$, and the horizontal dashed lines denote $J_p=J_c$.
• Figure 3: Pairing and exchange interaction strength versus the distance $d_s$, with $\mathcal{G}=1.2$ and $\theta_-=0.$
• Figure 4: A chain of $N$ equally spaced giant atoms coupled to a parametric waveguide, with no next-nearest-neighbor interactions in the chain.
• Figure 5: (a) Energy gap as a function of the giant atom frequency $\Delta_n$, with $J_p = 0.5$. (b) Energy gap as a function of the pairing interaction strength $J_p$, with $\Delta_n = 2.0$. (c) Fidelity susceptibility of the XY model versus atomic detuning $\Delta_n$, exhibiting pronounced peaks at the critical points $\Delta_n = \pm 4J_c$, where $J_p = 0.5$ and $\delta = 0.01$. (d) Fidelity susceptibility as a function of the pairing interaction strength $J_p$, for $\Delta_n = 2.0$ and $\delta = 0.01$. All results are obtained for a finite system of size $N = 16$, with the exchange interaction strength set to $J_c = 1$.