arXiv subjects

Mengxin Du

Publications and source records attributed to Mengxin Du.

3 recordsLinked to original sources

arXiv2025

Coherent matter wave emission from an atomtronic transistor

The atomtronic matter-wave triple-well transistor is theoretically predicted to exhibit current gain and act as a coherent matter-wave emitter. In this work, we investigate the dynamics of an atomtronic transistor composed of a triple-well potential -- source, gate, and drain -- modeled by the time-dependent Gross-Pitaevskii equation. We systematically explore the dependence of the drain population and the current on the source bias potential and the strength of the interatomic interaction. Our simulations reveal signatures of resonant tunneling when the source chemical potential aligns with discrete energy levels in the gate well, leading to coherent matter-wave emission in the drain. Contrary to previous many-body studies that predicted interaction-induced current gain via coupling to gate well modes, our results suggest that coherence in the drain is primarily governed by single-particle resonances, with no evident broadening from nonlinear coupling.

cond-mat.quant-gas↗

arXiv2024

Characterizing Quantum Codes via the Coefficients in Knill-Laflamme Conditions

Quantum error correction (QEC) is essential for protecting quantum information against noise, yet understanding the structure of the Knill-Laflamme (KL) coefficients $λ_{ij}$ from the condition $PE_i^\dagger E_j P = λ_{ij} P$ remains challenging, particularly for nonadditive codes. In this work, we introduce the signature vector $\vecλ(P)$, composed of the off-diagonal KL coefficients $λ_{ij}$, where each coefficient corresponds to equivalence classes of errors counted only once. We define its Euclidean norm $λ^*(P)$ as a scalar measure representing the total strength of error correlations within the code subspace defined by the projector $P$. We parameterize $P$ on a Stiefel manifold and formulate an optimization problem based on the KL conditions to systematically explore possible values of $λ^*$. Moreover, we show that, for $((n,K,d))$ codes, $λ^*$ is invariant under local unitary transformations. Applying our approach to the $((6, 2, 3))$ quantum code, we find that $λ^*_{\text{min}} = \sqrt{0.6}$ and $λ^*_{\text{max}} = 1$, with $λ^* = 1$ corresponding to a known degenerate stabilizer code. We construct continuous families of new nonadditive codes parameterized by vectors in $\mathbb{R}^5$, with $λ^*$ varying over the interval $[\sqrt{0.6}, 1]$. For the $((7, 2, 3))$ code, we identify $λ^*_{\text{min}} = 0$ (corresponding to the non-degenerate Steane code) and $λ^*_{\text{max}} = \sqrt{7}$ (corresponding to the permutation-invariant code by Pollatsek and Ruskai), and we demonstrate continuous paths connecting these extremes via cyclic codes characterized solely by $λ^*$. Our findings provide new insights into the structure of quantum codes, advance the theoretical foundations of QEC, and open new avenues for investigating intricate relationships between code subspaces and error correlations.

quant-ph↗

arXiv2023

Many-Body Anderson Metal-Insulator Transition using Kicked Quantum Gases

Understanding the interplay of interactions and disorder in quantum transport poses long-standing scientific challenges, with many-body quantum transport phenomena in high-dimensional disordered systems remaining largely unexplored experimentally. We utilize a momentum space lattice platform using quasi-periodically kicked ultracold atomic gases to experimentally investigate many-body effects on the three-dimensional Anderson metal-insulator transition. We observe interaction-driven sub-diffusion and a divergence of delocalization onset time on approaching the many-body phase boundary. Mean-field numerical simulations are in qualitative agreement with experimental observations.

cond-mat.quant-gas↗