Experimental realization of quantum Zeno dynamics for robust quantum metrology

Abstract

Quantum Zeno dynamics (QZD), which restricts the system's evolution to a protected subspace, provides a promising approach for protecting quantum information from noise. Here, we explore a practical approach to harnessing QZD for robust quantum metrology. By introducing strong inter-particle interactions during the parameter encoding stage, we overcome the typical limitations of previous QZD studies, which have largely focused on single-particle systems and faced challenges where QZD could interfere with the encoding process. We experimentally validate the proposed scheme on a nuclear magnetic resonance platform, achieving near-optimal precision scaling under amplitude damping in both parallel and sequential settings. Numerical simulations further demonstrate the scalability of the approach and its compatibility with other control techniques for suppressing more general types of noise. These findings highlight QZD as a powerful strategy for noise-resilient quantum metrology.

Figures (4)

• Figure 1: Principle of QZD and its implementation Strategy. (a) Schematic diagram of the QZE and QZD. Solid (dashed) arrows indicate allowed (forbidden) transitions, while the eye symbols represent frequent measurements on the system. (b) Modification of energy-level structure induced by the strong coupling $KH_c$, where $|\lambda_\text{max}\rangle,|\lambda_\text{max-1}\rangle,\dots,|\lambda_\text{min}\rangle$ denote eigenvectors of $H_\text{en}$ corresponding to the maximal, second maximal, $\dots,$ and minimal eigenvalues, respectively. In the limit $K\to\infty$, the Zeno subspace $\mathcal{H}_\text{opt}=\text{span}\{|\lambda_\text{min}\rangle,|\lambda_\text{max}\rangle\}$ is dynamically isolated, and transitions outside $\mathcal{H}_\text{opt}$ are suppressed.
• Figure 2: Conventional and QZD-based multi-qubit Ramsey interferometry. (a) and (b) show quantum circuits and schematic illustrations of the cases with and without QZD, respectively. QZD is realized via strong inter-qubit coupling during the encoding process. Colored boxes indicate different subspaces in the system's Hilbert space.
• Figure 3: Results of the QZD-based multi-qubit Ramsey experiments. (a) Explicit pulse sequence, where amplitude-damping noise is simulated via ensemble averaging, with $\xi_i^{L,m}$ denoting the amplitude of a transverse stochastic field. QZD is implemented through nearest-neighbor Ising interactions. (b) Experimental results for the parallel sensing setting. The red star marks the optimal encoding time $t_\text{opt}$. With this encoding time fixed, the corresponding estimation precision $\delta \omega$ as a function of $N$ is shown in the main panel. (c) Experimental results of a hybrid parallel and sequential setting with $N=4$ and $t=2T$. The theoretical precision of the parallel setting with $N=8$ and $t=T$ (black dashed line) serves as a precision benchmark. The density matrices of the final states are reconstructed via quantum state tomography, where $f$ denotes their fidelity with encoded noise-free GHZ state.
• Figure 4: Scalability of QZD-based quantum metrology scheme and its integration with dynamical decoupling. (a) Ramsey fringe amplitude at $t = 2T$ versus coupling strength $K$ for various system sizes $N$ (colored lines). The gray line marks the threshold amplitude 0.9; intersections define the minimum coupling $K_\text{th}$. Inset: The scaling behavior of $K_\text{th}$ with $N$, which is fitted by $K_\text{th} = c_1/N+c_2$ with $c_1=66.4,c_2=-4.4$. (b) QFI for ac field frequency estimation versus encoding time. QZD and DD are implemented via continuous strong coupling $K H_c^\text{Is}$ and periodic $\pi$-pulses along $x$, respectively (inset).