Zhi-Ming Tang

Ytterbium inner-shell optical clocks, based on transitions to the long-lived 4f135d6s2 (J = 2) state, are a promising platform for metrology and fundamental physics studies but have been hindered by inefficient state detection. We overcome this critical bottleneck by identifying the 593 nm transition as the optimal single-laser repumping pathway and developing a corresponding high-performance laser. A Pound–Drever–Hall lock to a 10-cm Fabry–Pérot cavity, with active drift cancellation via an ultra-stable 578 nm reference, achieves an instability <2.0 × 10−15 at 1000 s. Spectroscopy on the 431 nm inner-shell clock transitions using this laser yields a repumping efficiency of 93(5)%, confirming our theoretical prediction of ∼94% and demonstrating a decisive advance over prior low-efficiency or complex multi-laser approaches. This achievement resolves a key obstacle, enabling the realization of functional, ultra-stable Yb inner-shell optical lattice clocks.

We report improved performance of the ¹⁷¹ Yb optical lattice clocks at East China Normal University, achieving a total uncertainty of 4.4×10 ⁻¹⁸ for the Yb2 clock through high-precision synchronous frequency comparisons with the similar Yb1 clock. A 578 nm laser for the ¹ S ₀ – ³ P ₀ clock transition is cavity-stabilized using a newly developed ultra-stable laser system, featuring a reduced thermal-noise limit compared to its predecessor. Through systematic optimization, including suppression of technical noise in the laser system and detailed evaluation of frequency shifts, such as collision, blackbody radiation, lattice, and Zeeman shifts, we achieved stable clock-transition spectra for the m _F = ± 1/2 spin states using 400 ms interrogation pulses, obtaining a Fourier-limited linewidth of 2 Hz. Based on these optimizations, synchronous comparisons between two ¹⁷¹ Yb clocks enable a fractional frequency instability for each clock to average at a rate of 2.0×10 ⁻¹⁶ / τ , reaching 1.9 − 0.4 + 1.2 ×10 ⁻¹⁸ at 8000 s, which provides the resolution necessary for high-precision systematic evaluation. Furthermore, a complementary asynchronous comparison accounting for the Dick noise yields an instability of 4.0×10 ⁻¹⁸ at 8000 s. The combination of these high-precision comparisons and rigorous frequency shift evaluations validates the total systematic uncertainty below 5×10 ⁻¹⁸ .

We present systematic relativistic many-body calculations of multipole transition properties for singly charged aluminum ion (Al II) using a method that combines the configuration interaction and many-body perturbation theory (CI+MBPT). Our calculations cover the 103 lowest energy levels in Al II. For five key low-lying states (3s^{2 1}S₀, 3s3p ³P₀, 3s3p ³P₁, 3s3p ³P₂, 3s3p ¹P₁), we tabulate the transition wavelengths, reduced matrix elements, transition probabilities, and oscillator strengths for about 400 electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions arising from these levels. Our calculated values agree well with available experimental data and other high-precision theoretical calculations, with typical deviations on the order of 1%. Notably, we report over 80% of these transition lines as previously unreported, significantly expanding the existing spectroscopic database for Al II. These results can serve as a valuable reference resource for ongoing precision quantum metrology as well as astrophysical spectroscopy involving Al II ion.

We present systematic relativistic many-body calculations of multipole transition properties for singly charged aluminum ion (Al II) using a method that combines the configuration interaction and many-body perturbation theory (CI+MBPT). Our calculations cover the 103 lowest energy levels in Al II. For five key low-lying configurations (3s2 1S0, 3s3p 3P0, 3s3p 3P1, 3s3p 3P2, 3s3p 1P1), we tabulate the transition wavelengths, reduced matrix elements, transition probabilities, and oscillator strengths for about 400 electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions arising from these levels. Our calculated values agree well with available experimental data and other high-precision theoretical calculations, with typical deviations on the order of 1%. Notably, we report over 80% of these transition lines as previously unreported, significantly expanding the existing spectroscopic database for Al II. These results can serve as a valuable reference resource for ongoing precision quantum metrology as well as astrophysical spectroscopy involving Al II ion.

The X-ray spectra of L-shell transitions in Neon-like Xenon ion (Xe⁴⁴⁺) have been precisely measured at the Shanghai Electron-Beam Ion Trap using a high-resolution crystal spectrometer. Focusing on the line-intensity ratio of the 3F {2p⁶-(2p⁵_1/23s_1/2)_J=1} and 3D {2p⁶-(2p⁵_3/23d_5/2)_J=1} lines (3F/3D), our measurements have achieved remarkable precision improvements over the previous studies. These spectra have been simulated using the collisional-radiative model (CRM) within the Flexible Atomic Code, showing good agreement with the measurements. The previously reported discrepancies, approximately ranging from 10% to 20%, have been significantly reduced in this work to below 1.4% for electron-beam energies exceeding 6 keV and to around 7% for lower energies. Furthermore, our analysis of population fluxes of the involved levels reveals a very high sensitivity of the 3F line to radiation cascades. This suggests that the current CRM, which conventionally excludes interionic population transfer processes, may underestimate the population of the upper level of the 3F line and the cascade-related higher levels, thus explaining the remaining discrepancies. These findings provide a solid foundation for further minimizing these discrepancies and are crucial for understanding the atomic structure and plasma model of these ions.