arXiv subjects

Longsheng Ma

Publications and source records attributed to Longsheng Ma.

7 recordsLinked to original sources

arXiv2026

Th$^{4+}$ ion cluster structures and electric field gradients in $^{229}$Th:CaF$_2$

The low-energy nuclear isomeric transition of $^{229}$Th is a promising frequency reference for a solid-state nuclear optical clock. Wide-band-gap fluoride crystals such as CaF$_2$ offer transparent hosts for embedding Th nuclei at high density. Substitution of Th$^{4+}$ for Ca$^{2+}$ requires charge compensation, linking the local defect structure to nuclear quadrupole splitting. We use first-principles calculations to examine neutral Th dimers compensated by four interstitial F ions ($\mathrm{F}_{i}^{-}$). Screening different compensation geometries by their relative formation energies identifies a family of low-energy configurations with closely similar local structures. These configurations share large electric field gradients and small asymmetry parameters, consistent with the experimental high-EFG site 3. Their calculated quadrupole splittings are further compared with the measured C13 spectra. Together, the energetic and spectroscopic results support $\mathrm{F}_{i}^{-}$-compensated Th dimers as candidate microscopic structures for site 3 in Th:CaF$_2$.

cond-mat.mtrl-sci↗

arXiv2026

Optical Signals Synthesized from an Optical Lattice Clock with Uncertainty of 1.3E-17

We report an accurate optical frequency synthesizer, which can generate single-frequency laser light with high frequency stability and accuracy at desired frequencies over a wide optical region. The frequency of the output signal is divided from an 171Yb optical lattice clock via an accurate optical frequency divider based on an optical frequency comb. Therefore, the output of the optical frequency synthesizer inherits the frequency accuracy from the Yb optical clock. The frequency uncertainty of the 171Yb optical lattice clock is evaluated to be 6.8 mHz, corresponding to a fractional frequency uncertainty of 1.3E-17, mainly limited by the blackbody radiation shift and the lattice-induced light shift.

physics.optics↗

arXiv2026

A nuclear clock synchronized to $^{229}$Th

Atomic clocks have made time and frequency the most precisely measured quantities in physics, progressing from microwave standards that realize the SI second to optical clocks with unprecedented precision. A nuclear clock transfers the frequency reference from an electronic to a nuclear transition, and the uniquely low-lying, laser-accessible isomeric transition in $^{229}$Th currently offers the most practical route to compact, robust timekeeping and sensitive tests of fundamental physics. Realizing such a clock requires turning spectroscopy of the $^{229}$Th nuclear resonance into a stable discriminator for steering a traceable oscillator. Here we demonstrate a $^{229}$Th nuclear clock by stabilizing a continuous-wave, narrow-linewidth 148.4-nm vacuum-ultraviolet (VUV) laser to a resolved, weakly temperature-sensitive nuclear transition in $^{229}$Th$:$CaF$_2$ crystals. A $10$-$μ\mathrm{W}$ VUV source generated by four-wave mixing in cadmium vapour and phototube-based frequency-modulation absorption readout provide a fast, high-signal-to-noise nuclear discriminator. The clock reaches a fractional frequency instability of $5\times10^{-13}/\sqrt{τ/\mathrm{s}}$ for averaging time $τ$. Clock-transition frequencies measured in two independently fabricated crystals agree at the $10^{-13}$ level and are consistent with previous VUV-comb measurements on other $^{229}$Th:CaF$_2$ crystals. These results establish laser-addressed nuclei as operational clock references and provide a reproducible solid-state platform for compact nuclear clocks, nuclear quantum sensors and precision tests of fundamental physics.

physics.atom-ph↗

arXiv2024

Thorium doped strontium fluoride crystal: a unique candidate for solid nuclear optical clock material

We report a candidate with unique advantages in the cultivation of solid-state nuclear clock material, Th:SrF2 crystal. It not only has a segregation coefficient close to 1, which can achieve highly efficient and uniform doping of Th, but also ensures a high transmittance (~69% at 150 nm) while achieving extremely high doping concentration (232Th>6*10^20 cm^(-3). In addition, SrF2 crystal will not be irradiated-colored under strong α radiation like CaF2 crystal, Th:SrF2 crystal is expected to fully unleash its high concentration doping characteristics while ensuring its transmission performance in nuclear transition band not be severely affected by 229Th radiation damage.

cond-mat.mtrl-sci↗

arXiv2024

Miniature narrow-linewidth 1 μm Laser

Self-injection locking scheme has the potential to narrow the linewidth of lasers in a compact setup. Here, we report a narrow linewidth laser source near 1 μm by self-injection locking scheme using a Fabry-Perot (FP) hollow resonator with a high-quality factor (Q>10^8). The measured fundamental linewidth of the laser is 41 Hz, and a coarse tuning range over 5.5 nm is achieved by changing the driving current of the laser source. Meanwhile, a fine-tuning range of 373 MHz is achieved without mode hops by changing the voltage applied to the PZT on the resonator. More importantly, benefiting from the low thermal refractive noise and low thermal expansion of the FP hollow resonator, the beat-note linewidth and the frequency Allan deviation are measured to be 510.3 Hz in and 10^-11 (1s averaging time), respectively, by using a fully stabilized frequency comb as reference. Such a high-performance laser is fully integrated with a palm-sized package (52.3 mL) for field-deployable applications.

physics.optics↗

arXiv2016

Optical frequency divider with division uncertainty at the 10^(-21) level

Optical clocks with unprecedented accuracy of 10^(-18) will lead to innovations in many research areas. All the applications of optical clocks rely on the ability of precisely converting the frequency from one optical clock to another, or particularly to the frequencies in the fiber telecom band for long-distance transmission. Here, we report a low-noise, high precision optical frequency divider. It can realize accurate optical frequency conversion as well as enable precise measurement of optical frequency ratios. By comparing against the frequency ratio between the fundamental and the second harmonic of a 1064 nm laser rather than a second similar system, the optical frequency divider is demonstrated to have a frequency division instability of 6e-19 at 1 s and a fractional frequency division uncertainty of 1.4e-21, nearly three orders of magnitude better than the most accurate optical clocks. It allows optical clocks to be accessible to many precision measurement applications.

physics.optics↗

arXiv2006

Measurement of the Absorption Spectrum of water ion in the Visible Region

Together with the 74 lines belonging to (0,9,0)-(0,0,0) band, the high-resolution absorption spectrum of H2O+ was observed in the visible region of 16680 -17300 (cm-1) using optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy for the first time, which verifies the high sensitivity and high signal to noise ratio (S/N) of this technique.

physics.optics↗