arXiv subjects

Mengna Yang

Publications and source records attributed to Mengna Yang.

5 recordsLinked to original sources

arXiv2025

Enhancing the coherence time of a neutral atom by an optical quartic trap

The coherence time of an optically trapped neutral atom is a crucial parameter for quantum technologies. We found that optical dipole traps with higher-order spatial forms inherently offer lower decoherence rates compared to those with lower-order spatial forms. We formulated the decoherence rate caused by the variance of the differential energy shift and photon jumping rate. Then, we constructed blue-detuned harmonic and quartic optical dipole traps, and experimentally investigated the coherence time of a trapped single cesium atom. The experimental results qualitatively verified our theory. Our approach provides a novel method to enhance the coherence time of optically trapped neutral atoms.

quant-ph↗

arXiv2023

Extending the coherence time limit of a single-alkali-atom qubit by suppressing phonon-jumping-induced decoherence

In the fields of quantum metrology and quantum information processing with the system of optically trapped single neutral atoms, the coherence time of qubit encoded in the electronic states is regarded as one of the most important parameters. Longer coherence time is always pursued for higher precision of measurement and quantum manipulation. The coherence time is usually assumed to be merely determined by relative stability of the energy between the electronic states, and the analysis of the decoherence was conducted by treating the atom motion classically. We proposed a complete description of the decoherence of a qubit encoded in two ground electronic states of an optically trapped alkali atom by adopting a full description of the atomic wavefunction. The motional state, i.e., the phonon state, is taken into account. In addition to decoherence due to the variance of differential light shift (DLS), a new decoherence mechanism, phonon-jumping-induced decoherence (PJID), was discovered and verified experimentally. The coherence time of a single-cesium-atom qubit can be extended to $T_2\approx 20$ s by suppressing both the variances of DLS and PJID by trapping the atom in a blue-detuned bottle beam trap (BBT) and preparing the atom in its three-dimensional motional ground states. The coherence time is the longest for a qubit encoded in an optically trapped single alkali atom. Our work provides a deep understanding of the decoherence mechanism for single atom qubits and thus provides a new way to extend the coherence time limit. The method can be applied for other atoms and molecules, opening up new prospects for high-precision control the quantum states of optically trapped atoms or molecules.

quant-ph↗

arXiv2023

PointMoment:Mixed-Moment-based Self-Supervised Representation Learning for 3D Point Clouds

Large and rich data is a prerequisite for effective training of deep neural networks. However, the irregularity of point cloud data makes manual annotation time-consuming and laborious. Self-supervised representation learning, which leverages the intrinsic structure of large-scale unlabelled data to learn meaningful feature representations, has attracted increasing attention in the field of point cloud research. However, self-supervised representation learning often suffers from model collapse, resulting in reduced information and diversity of the learned representation, and consequently degrading the performance of downstream tasks. To address this problem, we propose PointMoment, a novel framework for point cloud self-supervised representation learning that utilizes a high-order mixed moment loss function rather than the conventional contrastive loss function. Moreover, our framework does not require any special techniques such as asymmetric network architectures, gradient stopping, etc. Specifically, we calculate the high-order mixed moment of the feature variables and force them to decompose into products of their individual moment, thereby making multiple variables more independent and minimizing the feature redundancy. We also incorporate a contrastive learning approach to maximize the feature invariance under different data augmentations of the same point cloud. Experimental results show that our approach outperforms previous unsupervised learning methods on the downstream task of 3D point cloud classification and segmentation.

cs.CV↗

arXiv2023

Resolved Raman sideband cooling of a single optically trapped cesium atom

We developed a resolved Raman sideband cooling scheme that can efficiently prepare a single optically trapped cesium (Cs) atom in its motional ground states. A two-photon Raman process between two outermost Zeeman sublevels in a single hyperfine state is applied to reduce the phonon number. Our scheme is less sensitive to the variation in the magnetic field than the commonly used scheme where the two outermost Zeeman sublevels belonging to the two separate ground hyperfine states are taken. Fast optical pumping with less spontaneous emission guarantees the efficiency of the cooling process. After cooling for 50 ms, 82% of the Cs atoms populate their three-dimensional ground states. Our scheme improves the long-term stability of Raman sideband cooling in the presence of magnetic field drift and is thus suitable for cooling other trapped atoms or ions with abundant magnetic sublevels.

quant-ph↗

arXiv2022

Convergence analysis of Jacobi spectral collocation methods for weakly singular nonlocal diffusion equations with volume constraints

This paper considers efficient spectral solutions for weakly singular nonlocal diffusion equations with Dirichlet-type volume constraints. The equation we consider contains an integral operator that typically has a singularity at the midpoint of the integral domain, and the approximation of the integral operator is one of the essential difficulties in solving nonlocal equations. To overcome this problem, two-sided Jacobi spectral quadrature rules are proposed to develop a Jacobi spectral collocation method for nonlocal diffusion equations. A rigorous convergence analysis of the proposed method with the $L^\infty$ norm is presented, and we further prove that the Jacobi collocation solution converges to its corresponding local limit as nonlocal interactions vanish. Numerical examples are given to verify the theoretical results.

math.NA↗