Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

NPG Asia Materials

Triplet-radical spin entanglement: potential of molecular materials for high-temperature quantum information processing

Lin Ma, Jiawei Chang, Qiuyuan Chen, Taoyu Zou, Wei Wu, Hai Wang

Published May 20, 2022• 10 citations
Publisher

Abstract

Abstract Recently, spin-bearing molecules have been experimentally demonstrated to have great potential as building blocks for quantum information processing due to their substantial advantages including tunability, portability, and scalability. Here, we propose a theoretical model based on the theory of open quantum systems for spin dynamics in a molecule containing one radical, which can interact with the triplet state arising from another part of the molecule owing to optical excitation and intersystem crossing. With the initial state being a classical mixture of a radical $$\frac{1}{2}$$ 1 2 -spin, the exchange interaction between the radical and the triplet produces a spin coherent state, which could potentially be used for a qubit-qutrit quantum entangling gate. Our calculations for the time-resolved electron paramagnetic resonance spectra showed good qualitative agreement with the related experimental results for radical-bearing molecules at high temperature (~77 K, the boiling point of liquid nitrogen). This work therefore lays a solid theoretical cornerstone for optically driven quantum gate operations in radical-bearing molecular materials, aiming toward high-temperature quantum information processing.

DOI
10.1038/s41427-022-00392-6

Related papers

Triplet-mediated spin entanglement between organic radicals: integrating first principles and open-quantum-system simulations

Tianhong Huang, Jiawei Chang, Lin Ma +5 more

Abstract Controlling molecular spin quantum bits optically offers the potential to effectively reduce decoherence and raise the working temperature of quantum computers. Here, exchange interactions and spin dynamics, as mediated by an optically driven triplet state, are calculated for a molecule that consists of a pair of radicals and represents a potential quantum-circuit building block. Consistent with the previous experimental observation of spin coherence induced by the triplet state, our work demonstrates an optically driven quantum gate operation scheme in a molecule. A technological blueprint combining a two-dimensional molecular network and programmable nanophotonics, both of which are sufficiently developed, is proposed. We thus realize computational exploration of chemical databases to identify suitable candidates for molecular spin quantum bits and couplers to be hybridized with nanophotonic devices. The work presented here is proposed to realize a new approach for exploring molecular excited states and click chemistry, toward advancing molecular quantum technology.

NPG Asia Materials•Dec 1, 2023•12 citations

Entanglement in a molecular Lieb-lattice quantum computing circuit: A tensor network study

Wei Wu

Here a finite-Lieb-lattice quantum computing circuit consisting of spin-1/2 quantum bits (qubits) and triplet couplers is designed. Important gradient - quantum entanglement - is analysed. This type of design could be realised in a vast range of molecules containing multiple radicals, in which the communications among qubits are controlled by the optically driven triplets. The von Neumann entanglement entropy, reduced density matrices, and spin-spin correlations were computed using tensor-network methods by varying the magnetic anisotropy and external magnetic field. This work uncovers the rich entanglement patterns, quantum phase transitions, and tunable spin coherence in this mixed spin system, designed for molecular spin-based quantum computing. These findings have important implications for triplet-mediated molecular self-assembly quantum computing circuit, especially for the entangling gate based on molecules. This work would provide a theoretical cornerstone for the experimental realisation of scalable molecule-based quantum computing circuits.

arXiv:2604.13093•Apr 8, 2026•0 citations

Blueprint of optically addressable molecular network for quantum circuit architecture

Chang, Jiawei, Tianhong Huang, Ma, Lin +3 more

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.

arXiv:2209.04835•Sep 11, 2022•1 citation

A Single-Molecule Spin-Photon Interface

Simon Roggors, Thomas Unden, Anna Aubele +12 more

Optical interfaces that connect long-lived spin qubits to photons are a central requirement for quantum networking and distributed quantum information processing. Currently, solid-state atomic defects are leading candidates due to their inherent spin and optical coherence. Building on these advancements, synthetically tailored molecular systems represent a fundamental change in the field, utilizing precise atomic control and consistent bottom-up assembly. However, the lack of a robust spin-photon interface combining bright fluorescence, high spectral stability, and the persistent spin lifetimes inherent to ground-state systems has prohibited the detection of individual molecular qubits. Here we show that a triplet ground state carbene molecule, embedded within a structurally matched host crystal, functions as a robust spin-photon interface with single-molecule addressability. The system exhibits narrow zero-phonon lines, spectral stability over more than an hour, spin-selective optical transitions and single-molecule optically detected magnetic resonance. Coherent control yields millisecond-scale dynamical-decoupling coherence and tens-of-milliseconds spin relaxation at a temperature of 4.5 K. These results establish molecular qubits as a viable platform for single-emitter quantum optics while preserving the advantages of bottom-up chemical design and processable materials.

quant-pharXiv:2605.10077•Nature•May 12, 2026•0 citations

Coherent manipulation and quantum phase interference in a fullerene-based electron triplet molecular qutrit

Ye‐Xin Wang, Zheng Liu, Yu‐Hui Fang +3 more

Abstract High-spin magnetic molecules are promising candidates for quantum information processing because their intrinsic multiplicity facilitates information storage and computational operations. However, due to the absence of suitable sublevel splittings, their susceptibility to environmental disturbances and limitation from the selection rule, the arbitrary control of the quantum state of a molecular electron multiplet has not been realized. Here, we exploit the photoexcited triplet of C70 as a molecular electron spin qutrit with pulsed electron paramagnetic resonance. We prepared the system into 3-level superposition states characteristic of a qutrit and validated them by the tomography of their density matrices. To further elucidate the coherence of the operation and the nature of the system as a qutrit, we demonstrated the quantum phase interference in the superposition. The interference pattern is further interpreted as a map of possible evolution paths in the space of phase factors, representing the quantum nature of the 3-level system.

arXiv:2007.09825•npj Quantum Information•Feb 15, 2021•35 citations

Entangling nuclear spins using photoexcited triplet states

Vasileia Filidou

Entanglement is one of the most technologically important quantum phenomena and its con-trolled creation brings us a step closer to the realisation of a quantum computer. Hybrid electron and nuclear spin systems which combine long nuclear decoherence times with the high polarisation and rapid processing times of electron spins are considered reliable candidates for the representation of the fundamental building block of a quantum computer, the qubit. In the literature electron spins quite often play the role of a mediator which can access, manipulate and couple states with long coherence times, beneficial for storing quantum information. Despite the fact that an electron spin can be a useful resource for nuclear spin systems, its permanent presence can be a source of decoherence. The use of transient photoexcited electron spins provide an additional advantage and once the operations which involve the electron spin are completed, the electron spin can decay and not interfere further with the evolution of the system. In this thesis we report magnetic resonance experiments and density functional theory calculations for the demonstration of nuclear - nuclear entanglement using photoexcited triplet states. We study homonuclear and heteronuclear fullerene derivatives and we identify in each case the relevant parameters that can lead to high fidelity entangling operations. The hyperfine interaction in a homonuclear system is the key parameter which determines the degree of entanglement between the nucelar spins according to a recent theoretical proposal. We measure and calculate the hyperfine interaction in homonuclear systems with 13C nuclear spins in order to prove the feasibility of this scheme. Further experiments on a fullerene system with two nuclear spins a 31P and a 1H show that entangling operations of high fidelity which involve the demonstration of CNOT gates, are possible within the lifetime of the triplet state.

•Jan 1, 2012•0 citations
Abstract Recently, spin-bearing molecules have been experimentally demonstrated to have great potential as building blocks for quantum information processing due to their substantial advantages including tunability, portability, and scalability. Here, we propose a theoretical model based on the theory of open quantum systems for spin dynamics in a molecule containing one radical, which can interact with the triplet state arising from another part of the molecule owing to optical excitation and intersystem crossing. With the initial state being a classical mixture of a radical 12\frac{1}{2}21​ 1 2 -spin, the exchange interaction between the radical and the triplet produces a spin coherent state, which could potentially be used for a qubit-qutrit quantum entangling gate. Our calculations for the time-resolved electron paramagnetic resonance spectra showed good qualitative agreement with the related experimental results for radical-bearing molecules at high temperature (~77 K, the boiling point of liquid nitrogen). This work therefore lays a solid theoretical cornerstone for optically driven quantum gate operations in radical-bearing molecular materials, aiming toward high-temperature quantum information processing.
Abstract Controlling molecular spin quantum bits optically offers the potential to effectively reduce decoherence and raise the working temperature of quantum computers. Here, exchange interactions and spin dynamics, as mediated by an optically driven triplet state, are calculated for a molecule that consists of a pair of radicals and represents a potential quantum-circuit building block. Consistent with the previous experimental observation of spin coherence induced by the triplet state, our work demonstrates an optically driven quantum gate operation scheme in a molecule. A technological blueprint combining a two-dimensional molecular network and programmable nanophotonics, both of which are sufficiently developed, is proposed. We thus realize computational exploration of chemical databases to identify suitable candidates for molecular spin quantum bits and couplers to be hybridized with nanophotonic devices. The work presented here is proposed to realize a new approach for exploring molecular excited states and click chemistry, toward advancing molecular quantum technology.
Here a finite-Lieb-lattice quantum computing circuit consisting of spin-1/2 quantum bits (qubits) and triplet couplers is designed. Important gradient - quantum entanglement - is analysed. This type of design could be realised in a vast range of molecules containing multiple radicals, in which the communications among qubits are controlled by the optically driven triplets. The von Neumann entanglement entropy, reduced density matrices, and spin-spin correlations were computed using tensor-network methods by varying the magnetic anisotropy and external magnetic field. This work uncovers the rich entanglement patterns, quantum phase transitions, and tunable spin coherence in this mixed spin system, designed for molecular spin-based quantum computing. These findings have important implications for triplet-mediated molecular self-assembly quantum computing circuit, especially for the entangling gate based on molecules. This work would provide a theoretical cornerstone for the experimental realisation of scalable molecule-based quantum computing circuits.
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.
Optical interfaces that connect long-lived spin qubits to photons are a central requirement for quantum networking and distributed quantum information processing. Currently, solid-state atomic defects are leading candidates due to their inherent spin and optical coherence. Building on these advancements, synthetically tailored molecular systems represent a fundamental change in the field, utilizing precise atomic control and consistent bottom-up assembly. However, the lack of a robust spin-photon interface combining bright fluorescence, high spectral stability, and the persistent spin lifetimes inherent to ground-state systems has prohibited the detection of individual molecular qubits. Here we show that a triplet ground state carbene molecule, embedded within a structurally matched host crystal, functions as a robust spin-photon interface with single-molecule addressability. The system exhibits narrow zero-phonon lines, spectral stability over more than an hour, spin-selective optical transitions and single-molecule optically detected magnetic resonance. Coherent control yields millisecond-scale dynamical-decoupling coherence and tens-of-milliseconds spin relaxation at a temperature of 4.5 K. These results establish molecular qubits as a viable platform for single-emitter quantum optics while preserving the advantages of bottom-up chemical design and processable materials.
Abstract High-spin magnetic molecules are promising candidates for quantum information processing because their intrinsic multiplicity facilitates information storage and computational operations. However, due to the absence of suitable sublevel splittings, their susceptibility to environmental disturbances and limitation from the selection rule, the arbitrary control of the quantum state of a molecular electron multiplet has not been realized. Here, we exploit the photoexcited triplet of C70 as a molecular electron spin qutrit with pulsed electron paramagnetic resonance. We prepared the system into 3-level superposition states characteristic of a qutrit and validated them by the tomography of their density matrices. To further elucidate the coherence of the operation and the nature of the system as a qutrit, we demonstrated the quantum phase interference in the superposition. The interference pattern is further interpreted as a map of possible evolution paths in the space of phase factors, representing the quantum nature of the 3-level system.
Entanglement is one of the most technologically important quantum phenomena and its con-trolled creation brings us a step closer to the realisation of a quantum computer. Hybrid electron and nuclear spin systems which combine long nuclear decoherence times with the high polarisation and rapid processing times of electron spins are considered reliable candidates for the representation of the fundamental building block of a quantum computer, the qubit. In the literature electron spins quite often play the role of a mediator which can access, manipulate and couple states with long coherence times, beneficial for storing quantum information. Despite the fact that an electron spin can be a useful resource for nuclear spin systems, its permanent presence can be a source of decoherence. The use of transient photoexcited electron spins provide an additional advantage and once the operations which involve the electron spin are completed, the electron spin can decay and not interfere further with the evolution of the system. In this thesis we report magnetic resonance experiments and density functional theory calculations for the demonstration of nuclear - nuclear entanglement using photoexcited triplet states. We study homonuclear and heteronuclear fullerene derivatives and we identify in each case the relevant parameters that can lead to high fidelity entangling operations. The hyperfine interaction in a homonuclear system is the key parameter which determines the degree of entanglement between the nucelar spins according to a recent theoretical proposal. We measure and calculate the hyperfine interaction in homonuclear systems with 13C nuclear spins in order to prove the feasibility of this scheme. Further experiments on a fullerene system with two nuclear spins a 31P and a 1H show that entangling operations of high fidelity which involve the demonstration of CNOT gates, are possible within the lifetime of the triplet state.