arXiv subjects

Ziqi Hu

Publications and source records attributed to Ziqi Hu.

6 recordsLinked to original sources

arXiv2025

Harnessing Chiral Spin States in Molecular Nanomagnets for Quantum Technologies

We present a theoretical framework to investigate spin chirality in molecular quantum systems. Focusing on a minimal three-spin-center model with antiferromagnetic exchange and symmetry breaking driven by an electric-field-induced Dzyaloshinskii-Moriya interaction and applied magnetic fields-give rise to chiral ground states characterized by nonzero scalar spin chirality, $χ= \textbf{S}_1\cdot(\textbf{S}_r\times \textbf{S}_2)$. The emergent chiral qubits naturally suppress always-on interactions that can not be switched off in weakly coupled qubits, as demonstrated through Liouville-von Neumann dynamics, which reveal phase difference in superposition states that form chiral qubits. To validate this framework, we examine realistic lanthanide complexes with radical-bridged magnetic centers, where spin-orbit coupling and asymmetric exchange facilitate chirality. Our findings establish spin chirality engineering as a promising strategy for mitigating always-on interaction in entangling two chiral qubits in molecular quantum technologies.

cond-mat.mes-hall↗

arXiv2024

Graphendofullerene: a novel molecular two-dimensional ferromagnet

Carbon chemistry has attracted a lot of attention by chemists, physicists and material scientists in the last decades. The recent discovery of graphullerene provides a promising platform for many applications due to its exceptional electronic properties and the possibility to host molecules or clusters inside the fullerene units. Herein, we introduce graphendofullerene, a novel molecular-based two-dimensional (2D) magnetic material formed by trimetallic nitrides clusters encapsulated on graphullerene. Through first-principles calculations, we demonstrate the successful incorporation of the molecules into the 2D network formed by C$_{80}$ fullerenes, which leads to a robust long-range ferromagnetic order with a Curie temperature (Tc) of 38 K. Additionally, we achieve a 45% increase in Tc by strain engineering. These findings open the way for a new family of molecular 2D magnets based on graphendofullerene for advanced technologies.

cond-mat.mtrl-sci↗

arXiv2024

A Unified MPC Strategy for a Tilt-rotor VTOL UAV Towards Seamless Mode Transitioning

Capabilities of long-range flight and vertical take-off and landing (VTOL) are essential for Urban Air Mobility (UAM). Tiltrotor VTOLs have the advantage of balancing control simplicity and system complexity due to their redundant control authority. Prior work on controlling these aircraft either requires separate controllers and switching modes for different vehicle configurations or performs the control allocation on separate actuator sets, which cannot fully use the potential of the redundancy of tiltrotor. This paper introduces a unified MPC-based control strategy for a customized tiltrotor VTOL Unmanned Aerial Vehicle (UAV), which does not require mode-switching and can perform the control allocation in a consistent way. The incorporation of four independently controllable rotors in VTOL design offers an extra level of redundancy, allowing the VTOL to accommodate actuator failures. The result shows that our approach outperforms PID controllers while maintaining unified control. It allows the VTOL to perform smooth acceleration/deceleration, and precise coordinated turns. In addition, the independently controlled tilts enable the vehicle to handle actuator failures, ensuring that the aircraft remains operational even in the event of a servo or motor malfunction.

eess.SY↗

arXiv2023

Lanthanide molecular nanomagnets as probabilistic bits

Over the decades, the spin dynamics of a large set of lanthanide complexes have been explored. Lanthanide-based molecular nanomagnets are bistable spin systems, generally conceptualized as classical bits, but many lanthanide complexes have also been presented as candidate quantum bits (qubits). Here we offer a third alternative and model them as probabilistic bits (p-bits), where their stochastic behavior constitutes a computational resource instead of a limitation. We present a modelling tool for molecular spin p-bits, we demonstrate its capability to simulate bulk magnetic relaxation data and ac experiments and to simulate a minimal p-bit network under realistic conditions. Finally, we go back to a recent systematic data gathering and screen the best lanthanide complexes for p-bit behavior, lay out the performance of the different lanthanide ions and chemical families and offer some chemical design considerations.

cond-mat.mes-hall↗

arXiv2022

Electrical two-qubit gates within a pair of clock-qubit magnetic molecules

Enhanced coherence in HoW$_{10}$ molecular spin qubits has been demonstrated by use of Clock Transitions (CTs). More recently it was shown that, while operating at the CTs, it was possible to use an electrical field to selectively address HoW$_{10}$ molecules pointing in a given direction, within a crystal that contains two kinds of identical but inversion-related molecules. Herein we theoretically explore the possibility of employing the electric field to effect entangling two-qubit quantum gates among two neighbouring CT-protected HoW$_{10}$ qubits within a diluted crystal. We estimate the thermal evolution of $T_1$, $T_2$, find that CTs are also optimal operating points from the point of view of phonons, and lay out how to combine a sequence of microwave and electric field pulses to achieve coherent control within a 2-qubit operating space that is protected both from spin-bath and from phonon-bath decoherence. Finally, we found a highly protected 1-qubit subspace resulting from the interaction between two clock molecules.

quant-ph↗

arXiv2021

Binding Sites, Vibrations and Spin-Lattice Relaxation Times in Europium(II)-based Metallofullerene Spin Qubits

To design molecular spin qubits with enhanced quantum coherence, a control of the coupling between the local vibrations and the spin states is crucial, which could be realized in principle by engineering molecular structures via coordination chemistry. To this end, understanding the underlying structural factors that govern the spin relaxation is a central topic. Here, we report the investigation of the spin dynamics in a series of chemically-designed europium(II)-based endohedral metallofullerenes (EMFs). By introducing a unique structural difference, i.e. metal-cage binding site, while keeping other molecular parameters constant between different complexes, these manifest the key role of the three low energy metal-based vibrations in mediating the spin-lattice relaxation times (T1). The temperature dependence of T1 can thus be normalized by the frequencies of these low energy vibrations to show an unprecedentedly universal behavior for EMFs in frozen CS2 solution. Our theoretical analysis indicates that this structural difference determines not only the vibrational rigidity but also spin-vibration coupling in these EMF-based qubit candidates.

physics.chem-ph↗