arXiv subjects

Ziwen Song

Publications and source records attributed to Ziwen Song.

4 recordsLinked to original sources

arXiv2026

Low-Latency Out-of-Core ANN Search in High-Dimensional Space

In-memory graph-based approximate nearest neighbor (ANN) search has superior search performance but incurs significant memory footprint. Disk-based methods reduce memory usage but suffer from high disk access latency. A common challenge is how to achieve low-latency search while significantly reducing memory footprint. In this paper, we propose SkipDisk, a disk-memory hybrid ANN search that significantly reduces memory footprint while achieving search latency comparable to or lower than in-memory method HNSW. By analyzing existing disk-based methods, we observed that disk access remains the primary bottleneck, and existing lower bound based filtering methods are two loose to effectively reduce disk access. Therefore, we design SkipDisk to achieve tight lower bound with low memory footprint to reduce the search latency. First, we design a dedicated pivot for each point to improve the lower bound of the triangle inequality for effective filtering. We further design an estimation-based approach based on this lower bound. Second, to reduce the memory footprint, we employ a three-level data pruning strategy to preserve informative data in memory. Third, to further reduce search latency, we design an asynchronous I/O strategy based on the decoupling of in-memory search and disk access by storing neighbor nodes in memory. Experiments show that our method achieves a latency of 85 of HNSW's latency with approximately 10 memory footprint, and a latency to 63 of HNSW's with a slightly higher memory footprint of around 20.

cs.DB↗

arXiv2026

Constraint-native quantum control for fidelity--complexity trade-offs with inexact proximal ADMM

Quantum-control pulses are often optimised for nominal fidelity before waveform constraints are imposed. This sequence can conceal the fidelity cost of producing smooth, band-limited, and amplitude-admissible controls. Here, we evaluate a constraint-native alternative based on inexact proximal alternating-direction updates. The formulation combines gate-infidelity minimisation with amplitude bounds, Fourier-domain bandwidth projection, amplitude sparsity, and total-variation regularisation. We compare it with GRAPE, standard Krotov optimisation, and L-BFGS-B on a single-qubit gate, a leakage-prone qutrit gate, and a two-qubit entangler without a directly controlled target generator. Random seeds are paired across methods, and qutrit computational-subspace fidelity is reported alongside leakage. PADMM-Warm reached mean qutrit and two-qubit fidelities of $0.6363$ and $0.9541$, respectively, while reducing total variation by factors of $13.2$ and $10.7$ relative to L-BFGS-B. These results define a reproducible fidelity--complexity trade-off, not a universal fidelity advantage. The method is therefore a numerical tool for exploring low-complexity control frontiers rather than a replacement for unconstrained high-fidelity solvers.

quant-ph↗

arXiv2026

Optimal Control Design of Robust Raman Pulses for High-Fidelity Cold-Atom Interferometry

The performance of high-precision cold-atom interferometers is often limited by imperfections in the Raman laser fields. We present a reproducible framework for robust Raman mirror-pulse design and compare Krotov, GRAPE, and CRAB under a common normalized peak-amplitude limit of 3.0. The effective two-level model uses a 25-member detuning--amplitude ensemble and a dense out-of-sample grid. In the fixed-budget study, GRAPE attained a terminal ensemble error of $1.224\times10^{-2}$ and projected Krotov attained $1.243\times10^{-2}$; Krotov occupied a slightly larger $P_e\ge0.9$ grid fraction (0.177 versus 0.170). The best of five CRAB seeds gave $3.081\times10^{-2}$. In the interferometer calculation, GRAPE produced the largest contrast, $0.582\pm0.019$, while Krotov and the selected CRAB pulse gave $0.454\pm0.019$ and $0.439\pm0.023$, respectively. These results establish a reproducible comparison of trade-offs, rather than universal superiority of any one optimizer.

physics.atom-ph↗

arXiv2025

Robust Atom Interferometry with Super-Gaussian Pulses against Thermal Velocity Spread

Laser frequency fluctuation and atomic thermal motion can lead to errors in pulse duration and detuning in cold atom interferometry, thereby reducing measurement stability and fringe contrast. To address this issue, we investigate the use of super-Gaussian pulses, which are characterized by smooth temporal profiles and centralized energy distribution, in the beam-splitting and reflection stages of an atom interferometer. Through numerical simulations, we compare the performance of rectangular, Gaussian, and 2nd- to 10th-order super-Gaussian pulses subject to deviations in pulse duration and detuning. Our results show that both Gaussian and super-Gaussian pulses offer a significant advantage over traditional rectangular pulses, particularly under thermal conditions where velocity spread is prominent. We find that 4th-order pulses achieving up to a 90\% improvement in contrast over rectangular pulses under realistic conditions, and while their peak performance at very low temperatures is comparable to that of Gaussian pulses, they demonstrate enhanced robustness against combined detuning and pulse-length errors. These findings demonstrate that super-Gaussian pulse shaping is an effective method for enhancing the robustness of atom interferometers against errors induced by thermal motion.

physics.atom-ph↗