arXiv subjects

Jiawei Chang

Publications and source records attributed to Jiawei Chang.

7 recordsLinked to original sources

arXiv2026

Quantum Coherence Governs Macroscopic Polymorphism in Organic Semiconductors

Polymorphism in organic semiconductors is conventionally framed as equilibrium thermodynamic selection, yet atmospheric-pressure vapor deposition routinely produces metastable phases that defy classical nucleation theory. We develop a symmetry-resolved open quantum system formulation of quantum dissipative assembly (QDA), in which the fundamental assembly unit is a vibronic wavepacket whose internal degrees of freedom are classified by the irreducible representations of the molecular point group. The carrier-gas environment acts as a structured dissipative bath with irrep-resolved spectral densities, and polymorph selection corresponds to relaxation into a symmetry-resolved maximum-transmittance attractor (MTA) rooted in quantum scattering theory and impedance matching. Guided by this theory, we tune the carrier-gas dissipative environment via reactor geometry, flow velocity, and precursor concentration to selectively synthesize a previously unreported polar polymorph of copper phthalocyanine, omega-CuPc, crystallizing in space group P2 with a dimerized bilayer superstructure and an extreme Davydov splitting of 154 nm. Further structural refinement with a 4-molecule modulated supercell model resolves the majority of discrepancies between powder X-ray diffraction and energy minimization, revealing secondary layer orientation modulation as a higher-order dissipative optimization product. The framework consistently explains the formation windows of the eta, alpha, and beta polymorphs, their distinct morphologies, and the marked difference in crystalline order between open-shell CuPc and closed-shell NiPc. Our findings establish a symmetry-guided, environment-controlled polymorph engineering strategy rooted in QDA, where the carrier-gas atmosphere serves as an active dissipative medium shaping the symmetry-resolved dissipative landscape rather than acting as an inert thermal bath.

physics.chem-ph↗

arXiv2025

Effect of a horizontal magnetic field on the melting of low Prandtl number liquid metal in a phase-change Rayleigh-B\'enard system

We investigated the low Prandtl number Rayleigh-B\'enard (RB) system with a melting top boundary under horizontal magnetic fields. This study is crucial to gain physical insights into the melting dynamics of thermal storage systems, which will help in controlling them. A three-dimensional solid-liquid phase change Rayleigh-B\'enard system of gallium was numerically simulated using the enthalpy-porosity method in a cubic domain. In the absence of a magnetic field, the melting process was clearly divided into four regimes: conduction, stable growth, coarsening, and chaotic regimes. We analyzed the flow and heat transfer characteristics in each regime and established scaling relations for the Nusselt number and liquid fraction. Under horizontal magnetic fields, a quasi-two-dimensional (Q2D) flow pattern was observed. We further examined the effects of magnetic field strength on different melting regimes. With increasing Hartmann number, a new flow mode emerged during the stable growth regime. The results also show that the magnetic field alters the relative duration of each melting regime in the overall melting process.

physics.flu-dyn↗

arXiv2024

Ultrafast Photocurrent Hysteresis in Photoferroelectric α-In2Se3

The photon-electron interactions are generally volatile and the intricate multiphysics details of photoexcited carrier dynamics are not yet distinguished. How to nonvolatile control the physical state through all-optical means and clarify the intricate physical processes has been a long-term goal pursued in polar materials. Photoferroelectric α-In2Se3 holds the great potential for capturing multimodal nonvolatile states due to the spontaneous reversible in-plane and out-of-plane polarizations and its tunable light-matter interactions arising from the electronic degree of freedom. Here we uncover a nonvolatile zero-bias ultrafast photocurrent hysteresis response with an all-optical scheme, diagnosed by in-plane and out-of-plane terahertz waves emitted from the photoferroelectric α-In2Se3. The mechanism of such ultrafast photocurrent hysteresis emerges as a result of anomalous bulk linear and circular photovoltaic effect synchronously driven by local polarization rearrangement. Utilizing anisotropic ferroelectric kinetics-induced relative phase between the in-plane and out-of-plane directions, we further show flexibly selective chirality, tunable rotational angle, and optimizable ellipticity of terahertz wave polarizations. Our finding offers a promising avenue towards direct ultrafast nonvolatile processing of photocurrent signals through an all-optical scheme.

physics.optics↗

arXiv2023

The insertion method to invert the signature of a path

The signature is a representation of a path as an infinite sequence of its iterated integrals. Under certain assumptions, the signature characterizes the path, up to translation and reparameterization. Therefore, a crucial question of interest is the development of efficient algorithms to invert the signature, i.e., to reconstruct the path from the information of its (truncated) signature. In this article, we study the insertion procedure, originally introduced by Chang and Lyons (2019), from both a theoretical and a practical point of view. After describing our version of the method, we give its rate of convergence for piecewise linear paths, accompanied by an implementation in Pytorch. The algorithm is parallelized, meaning that it is very efficient at inverting a batch of signatures simultaneously. Its performance is illustrated with both real-world and simulated examples.

stat.ME↗

arXiv2023

Blueprint of optically addressable molecular network for quantum circuit architecture

Optically connecting quantum bits can effectively reduce decoherence and facilitate long-distance communication. Optically addressable spin-bearing molecules have been demonstrated to have a good potential for quantum computing. In this report optically induced exchange interactions and spin dynamics, which are inherently important for spin-based quantum computing, have been calculated for a bi-radical - a potential quantum computing circuit unit. Consistent with the previous experimental observation of spin coherence induced by optical excitation, our work demonstrated an optically driven quantum gate operation scheme, implying a great potential of molecular quantum-circuit network. A blueprint of quantum circuit, integrating two-dimensional molecular network and programmable nano-photonics, both of which have been under extensive investigations and rather mature, was proposed. We thus envisage computational exploration of chemical database to identify suitable candidates for molecular spin quantum bit and coupler, which could be optimally integrated with nano-photonic devices to realize quantum circuit. The work presented here would therefore open up a new direction to explore 'Click Chemistry' for quantum technology.

quant-ph↗

arXiv2019

Insertion algorithm for inverting the signature of a path

In this article we introduce the insertion method for reconstructing the path from its signature, i.e. inverting the signature of a path. For this purpose, we prove that a converging upper bound exists for the difference between the inserted n-th term and the (n+1)-th term of the normalised signature of a smooth path, and we also show that there exists a constant lower bound for a subsequence of the terms in the normalised signature of a piecewise linear path. We demonstrate our results with numerical examples.

math.PR↗

arXiv2016

Signature inversion for monotone paths

The aim of this article is to provide a simple sampling procedure to reconstruct any monotone path from its signature. For every N, we sample a lattice path of N steps with weights given by the coefficient of the corresponding word in the signature. We show that these weights on lattice paths satisfy the large deviations principle. In particular, this implies that the probability of picking up a "wrong" path is exponentially small in N. The argument relies on a probabilistic interpretation of the signature for monotone paths.

math.PR↗