arXiv subjects

Juan Aragó

Publications and source records attributed to Juan Aragó.

4 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↗

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↗

arXiv2021

Spectroscopic analysis of vibronic relaxation pathways in molecular spin qubit $[$Ho(W$_5$O$_{18}$)$_2]^{9-}$: sparse spectra are key

Molecular vibrations play a key role in magnetic relaxation processes of molecular spin qubits as they couple to spin states, leading to the loss of quantum information. Direct experimental determination of vibronic coupling is crucial to understand and control the spin dynamics of these nano-objects, which represent the limit of miniaturization for quantum devices. Herein, we measure the vibrational properties of the molecular spin qubit $[$Ho(W$_5$O$_{18}$)$_2]^{9-}$ by means of magneto-infrared spectroscopy. Our results allow us to unravel the vibrational decoherence pathways in combination with $ab$ $initio$ calculations including vibronic coupling. We observe field-induced spectral changes near 63 and 370 cm$^{-1}$ that are modeled in terms of $f$-manifold crystal field excitations activated by odd-symmetry vibrations. The overall extent of vibronic coupling in this system is limited by a transparency window in the phonon density of states that acts to keep the intramolecular vibrations and $M_J$ levels apart. These findings advance the understanding of vibronic coupling in molecular magnets, place significant constraints on the pattern of crystal field levels in these systems, and provide a strategy for designing molecular spin qubits with improved coherence lifetimes.

cond-mat.mes-hall↗