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Tetrathiafulvalene-Based Molecular Qubit Frameworks with Room-Temperature Quantum Coherence

Aimei Zhou, Yanpei Lv, Yingchao Wang, J C Zhang, Lei Sun

Published Jul 26, 2026• 0 citations
Publisher

Abstract

Molecular qubits, owing to their designability and tunability, have emerged as fundamental units for quantum technologies. Among them, molecular qubit frameworks (MQFs) offer unique advantages in long-range ordered lattices and microporosity that provide well-defined phonon environments and guest-tunable spin dynamics. These features greatly enhance qubit performance and enable room temperature quantum operations, holding promise for quantum sensing applications. Herein, we compare the qubit performance of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and tetrathiafulvalene tetrabenzoic acid (H4TTFTB), which form stable radicals upon spontaneous oxidation in the air. We found that optical phonons dominate spin relaxation in HHTP, whereas H4TTFTB exhibits stronger spin-orbit coupling and higher acoustic phonon population that account for its shorter spin relaxation time. Meanwhile, H4TTFTB features a nuclear-spin-free core and in turn a prolonged phase memory time, making it a favorable qubit candidate. Furthermore, we synthesized three MQFs using H4TTFTB as the ligand, which not only retain the superior room-temperature qubit performance but also possess porous channels, establishing a viable platform for future quantum information applications.

DOI
10.26434/chemrxiv.15006560/v1

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Molecular qubits, owing to their designability and tunability, have emerged as fundamental units for quantum technologies. Among them, molecular qubit frameworks (MQFs) offer unique advantages in long-range ordered lattices and microporosity that provide well-defined phonon environments and guest-tunable spin dynamics. These features greatly enhance qubit performance and enable room temperature quantum operations, holding promise for quantum sensing applications. Herein, we compare the qubit performance of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and tetrathiafulvalene tetrabenzoic acid (H4TTFTB), which form stable radicals upon spontaneous oxidation in the air. We found that optical phonons dominate spin relaxation in HHTP, whereas H4TTFTB exhibits stronger spin-orbit coupling and higher acoustic phonon population that account for its shorter spin relaxation time. Meanwhile, H4TTFTB features a nuclear-spin-free core and in turn a prolonged phase memory time, making it a favorable qubit candidate. Furthermore, we synthesized three MQFs using H4TTFTB as the ligand, which not only retain the superior room-temperature qubit performance but also possess porous channels, establishing a viable platform for future quantum information applications.
One of the main challenges facing quantum information science (QIS) is the development of robust qubits that can be operated under ambient conditions. Current state-of-the-art anionic nitrogen-vacancy center (NV – ) defect qubits are robust enough to be operated at room temperature but lack scalability and tunability. These are areas where molecular qubits excel, although, in contrast, they typically suffer from poor air stability and fast decoherence at elevated temperatures and in magnetically noisy environments. Organic-based systems offer possible advantages to this end, although examples retaining room temperature coherence are still rare. Furthermore, most organic-based systems lack optical transitions similar to NV – centers that could allow for optical initialization and readout. Here we report two new organic-based qubit candidates that demonstrate room temperature coherence in nuclear and electron spin-rich environments. These qubits luminesce far into the near-infrared (NIR, 700–1700 nm) and telecom (∼1260–1625 nm) regions, ideal for biological sensing and communications applications, respectively.
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There are several important solid-state systems, such as defects in solids, superconducting circuits and molecular qubits, for attractive candidates of quantum computations. Molecular qubits, which benefit from the power of chemistry for the tailored and inexpensive synthesis of new systems, face the challenge from decoherence effect. The decoherence effect is due to the molecular qubits' inevitable interactions to their environment. Strategies to overcome decoherence effect have been developed, such as designing a nuclear spin free environment and working at atomic clock transitions. These chemical approaches, however, have some fundamental limitations. For example, chemical approach restricts the ligand selection and design to ligands with zero nuclear magnetic dipole moment, such as carbon, oxygen, and sulfur. Herein, a physical approach, named Dynamical decoupling (DD), is utilized to combat decoherence, while the limitations of the chemical approaches can be avoided. The phase memory time T2T_2T2​ for a transition metal complex has been prolonged to exceed one millisecond (1.4 1.4~1.4 ms) by employing DD. The single qubit figure of merit $Q_M $ reaches $ 1.4\times 10^5$, which is 404040 times better than that previously reported value for such system. Our results show that molecular qubits, with milliseconds T2T_2T2​, are promising candidates for quantum information processing.
The feasibility of active pre-cooling (APC) by temporarily over-coupling microwave cavity modes to a low-noise amplifier acting as an active cold load was demonstrated, offering an effective method to reduce thermal photon occupancy without cryogenic cooling. The potential of the organic radical BDPA as a tunable qubit medium with remarkably long spin-lattice and spin coherence relaxation times was assessed, comparing favorably with state-of-the-art molecular qubit media. A high-quality surface acoustic wave device integrated with pentacene-deposited molecular thin films was developed to achieve heterogeneous optically-detected spin acoustic resonance (HODSAR), enabling efficient zero-field spin control at room temperature via spin-phonon coupling. Through the construction of specialized experimental setups, the effectiveness of these techniques was demonstrated, facilitating pre-cooling of cavity modes, enhancing coherence times in qubit media, and achieving precise spin manipulation. While APC offers advantages over methods like masers and anti-masers, challenges such as the need for fast, low-loss microwave switches remain. The BDPA radicals showed significant promise for spin ensemble, and the SAW-based HODSAR device provides a scalable platform for spin manipulation in quantum technologies.
Metal-organic frameworks (MOFs) have emerged as promising candidates for quantum information and photonic applications due to their structural tunability and the potential to contain molecular qubits in architectures that support coherent light-matter interactions. In this study, we investigate the ultrafast coherent dynamics of a perylene-based MOF, UMCM-313, and its corresponding perylene-based organic linker crystal using time-resolved two-photon near-field scanning optical microscopy (NSOM). By tracking the electronic quantum coherence, we reveal coherent modes persisting up to several hundred femtoseconds (fs) at room temperature and extending to the picosecond regime (≈0.9-1 ps) at 173 K in the MOF, significantly longer than the coherence time observed in the organic linkers at the femtosecond scale. The enhanced electronic coherence of UMCM-313 is attributed to periodic chromophore separation and a reduced degree of homogeneous broadening. Because electron spin coherence can be several orders of magnitude longer than optical coherence, we further probed the spin coherence of photoexcited triplet states in UMCM-313 by using time-resolved and pulsed electron paramagnetic resonance (TREPR and pulse-EPR) spectroscopy. TREPR spectra reveal multiple triplet species within the framework, while pulse-EPR measurements yield a phase memory time of 237 ± 5 ns at 173 K. These results demonstrate that UMCM-313 supports both extended excitonic coherence and nanosecond spin coherence, underscoring the importance of periodic framework connectivity in sustaining phase-stable quantum states. The coexistence of electronic coherence and long-lived spin coherence highlights the potential of MOFs as hybrid platforms for quantum photonic and spintronic technologies capable of maintaining coherence under operationally accessible conditions.
ABSTRACT This review classifies qubit platforms from the perspective of quantum battery applications as inorganic, molecular, and organic material families using an energy‐based approach. The systems are compared in terms of energy level tunability, decoherence mechanisms, and environmental sensitivity. Superconducting and silicon spin qubits stand out with their high control accuracy and long decoherence times (on the order of seconds in purified silicon); however, the need for cryogenic operation and fixed energy levels limits them. In contrast, molecular (lanthanide and transition‐metal complexes) and organic (radical/polymer) systems offer atomically precise tunable energy levels through ligand engineering and chemical design and operate under near‐room temperature conditions. The study evaluates qubit platforms not only in terms of information processing but also with battery‐focused metrics such as energy capacity, charge power, ergotropy, storage lifetime, and quantum advantage arising from entanglement and collective interactions. Thus, molecular and organic systems stand out as the most promising candidates for quantum batteries due to their chemical tunability and bulk charging potential; the study presents a materials‐based roadmap combining quantum computing with energy storage.