arXiv subjects

Z. -H. Zhang

Publications and source records attributed to Z. -H. Zhang.

4 recordsLinked to original sources

arXiv2026

Learning quantum disentanglement scheduling from reduced states via modular hybrid policies

Quantum control with restricted state access is central to near-term quantum devices, where full wave-function information is unavailable. We study this problem through multiqubit disentanglement scheduling from partial observations, where a controller receives only two-qubit reduced density matrices and selects which qubit pair to disentangle at each step. We introduce a modular hybrid quantum--classical policy framework consisting of classical preprocessing, a parameterized quantum circuit as a compact nonlinear latent block, and classical postprocessing for pair-selection probabilities. Benchmarking 4-, 5-, and 6-qubit tasks, we find that preprocessing is the dominant factor governing performance under reduced-state observations, while the quantum module provides a conditional compact representation whose utility depends on the input features and model budget. We further identify a performance--efficiency trade-off across policy families and find that increasing circuit width is generally more useful than increasing depth. These results provide practical design principles for hybrid policies in reduced-information quantum control.

quant-ph↗

arXiv2014

Probing the mass degeneracy of particles with different spins

The spin is an important property of a particle. Although it is unlikely to happen, there is still a possibility that two particle with different spins share similar masses. In this paper, we propose a method to probe this kind of mass degeneracy of particles with different spins. We will use the cascade decay $B^+\to X(3872)K^+$, $X(3872)\to D^+D^-$ to explain our method. It can be seen that the possible mass degeneracy of $X(3872)$ can lead interesting behavior in the corresponding cascade decay.

hep-ph↗

arXiv2012

Investigations of the EPR parameters for the tetrahedral [FeX_4]^- clusters in AgX (X=Cl, Br)

The EPR parameters g factors and the superhyperfine parameters for the tetrahedral [FeX_4]^- clusters in AgX (X=Cl, Br) are theoretically investigated from the perturbation formulas of these parameters for a 3d^5 ion under tetrahedra by considering both the crystal-field and charge transfer contributions. The related model parameters are quantitatively determined from the cluster approach in a uniform way. The g-shift Δg (=g-g_s, where g_s\approx 2.0023 is the spin only value) from the charge transfer contribution is opposite (positive) in sign and much larger in magnitude as compared with that from the crystal-field one. The importance of the charge transfer contribution increases rapidly with increasing the covalency and the spin-orbit coupling coefficient of the ligand and thus exhibits the order of AgCl<AgBr. The unpaired spin densities of the halogen ns, npσ and npπ orbitals are quantitatively determined from the related molecular orbital coefficients based on the cluster approach.

cond-mat.mtrl-sci↗

arXiv2007

Direct CP violation in $\bar{B}^0 \to ρ^0(ω)ρ^0(ω) \to π^+π^-π^+π^-$

We study the direct CP violation in $\bar{B}^0 \to ρ^0(ω)ρ^0(ω) \to π^+π^-π^+π^-$ (with unpolarized $ρ^0(ω)$) via the $ρ-ω$ mixing mechanism which causes a large strong phase difference and consequently a large CP violating asymmetry when the masses of the $π^+π^-$ pairs are in the vicinity of the $ω$ resonance. Since there are two $ρ(ω)$ mesons in the intermediate state $ρ-ω$ mixing contributes twice to the first order of isospin violation, leading to an even larger CP violating asymmetry (could be 30% -- 50% larger) than in the case where only one $ρ(ω)$ meson is involved. The CP violating asymmetry depends on the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements and the hadronic matrix elements. The factorization approach is applied in the calculation of the hadronic matrix elements with the nonfactorizable effects being included effectively in an effective parameter, $N_c$. We give the constraint on the range of $N_c$ from the latest experimental data for the branching ratios for $\bar{B}^0 \toρ^0ρ^0$ and $\bar{B}^0 \toρ^+ρ^-$. We find that the CP violating asymmetry could be very large (even more than 90% for some values of $N_c$). It is shown that the sensitivity of the CP violating asymmetry to $N_c$ is large compared with its smaller sensitivity to the CKM matrix elements. We also discuss the possibility to remove the mod $(π)$ ambiguity in the determination of the CP violating phase angle $α$ through the measurement of the CP violating asymmetry in the decay $\bar{B}^0\to ρ^0(ω)ρ^0(ω) \to π^+π^-π^+π^-$.

hep-ph↗