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

arXiv:2607.16466

Host-guest Crystal Engineering Tailors the Room Temperature Spin Dynamics in Molecular Quantum Devices

Ziqiu Huang, Angus Cowley-Semple, Irena Nevjestic, Yifan Yu, Mark Oxborrow, Sam L. Bayliss, Sarah K. Mann, Max Attwood

quant-phphysics.chem-phSubmitted Jul 17, 2026• Announced Jul 21, 2026
arXivHTMLPDF

Abstract

Molecular materials that enable coherent control over an electron's spin state at room temperature are promising candidates for quantum technologies, including quantum sensors and ultra-low noise microwave amplifiers, known as masers. Host-guest molecular crystals enable independent control of spin-active guests and their local environments to enhance molecular spin properties and so improve device performance. Using electron paramagnetic resonance and optically-detected magnetic resonance, we demonstrate the ability to tune triplet population, depopulation, and spin-lattice relaxation by modulating host-dependent lattice rigidity and vibrational coupling to significantly reduce the operating requirements for building useful masers. Importantly, the most rigid host, picene, reveals the ability to slow spin-lattice relaxation without lengthening triplet lifetime, though at the cost of strain-induced line width broadening and reduced triplet spin polarisation. We also find that deuteration reduces the triplet resonance line width and vibrationally-mediated triplet depopulation. Consequently, we find that perdeuterated pentacene in perdeuterated p-terphenyl is the most viable candidate for building a continuous wave maser. This work demonstrates host-guest engineering as an important and practical method for tuning the spin-dependent performance of room-temperature molecular quantum technologies.

Comments
12 pages, 7 figures

Related papers

Room-temperature quantum-sensing molecular crystals grown in minutes

Madhur Parashar, Guangzhao Chen, Emanuel Druga +3 more

Quantum sensing increasingly demands materials combining room-temperature optical spin addressability and coherent control with rapid, accessible fabrication. Yet semiconductor platforms require costly materials and specialized processing, while molecular systems often depend on bespoke synthesis or involved crystal growth. Here we apply microspacing in-air sublimation (MAS) to rapidly fabricate quantum-sensing materials within minutes. Microgram quantities of commercially available precursors crystallize on glass, in air and without vacuum or inert-gas handling. Monitored in situ, growth yields optically clear, stoichiometric single crystals of excellent quality, including plates and needles with intrinsic optical waveguiding. Donor-acceptor charge-transfer co-crystals pairing anthracene or biphenyl with tetracyanobenzene, together with localized-exciton pentacene:pentacenequinone (P:PQ), exhibit room-temperature optically detected magnetic resonance (ODMR). Charge-transfer ODMR resonances reach linewidths below $4\mathrm{MHz}$, consistent with motional narrowing of mobile triplet excitons, while P:PQ supports coherent ensemble spin control with $T_2=0.56μ\mathrm{s}$. Functionality across chemically and electronically distinct pairs establishes MAS as an accessible screen for molecular quantum-sensing materials, connecting molecular crystal engineering with low-cost, chemically tunable thin triplet-spin layers and waveguiding sensor geometries for quantum sensing and microscopy.

quant-pharXiv:2609.30899•Sep 28, 2026

Room-temperature quantum devices: innovations in active pre-cooling protocol, spin-phonon coupling devices, and stable molecular spins

Kuan-Cheng Chen

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.

•Nov 4, 2024•0 citations

Understanding the spin coherence of molecular photoexcited triplet states from first principles

Ecaterina Păunică, Sam L. Bayliss

Optically readable molecular spins are attractive as quantum sensors due to their nanoscale modularity, synthetic tunability, and scope for sensitive readout. In particular, photoexcited spin-triplet states in organic molecules are appealing in supporting high optical-spin contrast at room temperature. Their utility is underpinned by their coherence, which warrants a detailed understanding of it. Here, from first principles, we systematically explore the Hahn-echo decoherence of the benchmark molecular system for room-temperature optically detected spin coherence---pentacene guest molecules coupled to a para-terphenyl host. Using generalized cluster-correlation expansion methods, we investigate the mechanisms of nuclear-spin-induced decoherence from zero to high magnetic field, exploring the role of guest vs host molecules, specific nuclei, zero-field splitting interactions, and hyperfine parameters. We describe how zero-field decoherence is driven by ~6 nuclei on the guest, while high-field decoherence is driven by ~600 nuclei in the host; how the longitudinal zero-field splitting parameter, $D$, can prolong $T_2$; and the magnetic-field-dependent processes which drive decoherence. These results advance our understanding of decoherence in optically readable molecular spins, providing insight for their synthetic enhancement and deployment as quantum probes.

quant-pharXiv:2609.16851•Sep 16, 2026

Dense pentacene cocrystal demonstrates room-temperature coherent control

Noella D'Souza, Guangzhao Chen, Madhur Parashar +13 more

Maximizing the number of addressable spins within a fixed volume can improve ensemble quantum sensor sensitivity, but dense packing usually increases dipolar interactions and excited-state transport, shortening coherence and suppressing optical readout. Here we report a 2:1 cocrystal of 6,13-dihydropentacene and pentacene (DHP/Pc) containing 33.3 mol% pentacene ($3.3\times10^{5}$ ppm; $9.51\times10^{20}$ cm$^{-3}$), a volumetric spin-site density more than two orders of magnitude above previous benchmarks, NV-diamond and pentacene-doped p-terphenyl (PDP). Despite this density, DHP/Pc exhibits microsecond spin coherence, room-temperature optically detected magnetic resonance and coherent control. Time-resolved measurements indicate that the long-lived triplet population is generated predominantly by intersystem crossing and exhibits strong, non-thermal sublevel polarization. Density-functional theory calculations further suggest that the native cocrystal geometry weakens electronic coupling between neighboring pentacenes, while the higher DHP triplet energy creates a barrier to triplet migration. These results identify molecular packing and coformer triplet energetics as complementary design parameters for preserving coherence in high spin-site density systems, demonstrating cocrystallization as a promising route to dense, optically addressable spin materials for room-temperature ensemble quantum sensing.

quant-pharXiv:2609.28912•Sep 25, 2026

Invasive optical pumping for room-temperature masers, time-resolved EPR, triplet-DNP, and quantum engines exploiting strong coupling

Hao Wu, Shamil Mirkhanov, Wern Ng +3 more

We explore an approach for optically pumping a body of optically dense magnetic material. This challenge arises in time-resolved electron paramagnetic resonance (TREPR), triplet-based dynamic nuclear polarisation (DNP), and cavity QED. Crystals of pentacene-doped p-terphenyl were grown around variously shaped ends of optical waveguides, through which pump light could be injected deeply into the crystal. When incorporated into a maser as the gain medium, we found that, compared to conventional side-pumping, 11 times less pump beam intensity was needed to reach the masing threshold and 54 times more pulse energy could be absorbed by the gain medium without damage, resulting in a record peak output power of -5 dBm.

Optics Express•Sep 2, 2020•6 citations

On-chip Radio Frequency Maser

Hongliang Wu, Zhengtao Wang, Yuchen Han +6 more

Room-temperature solid-state masers offer exceptional frequency selectivity and ultra-low noise for weak-signal detection. However, their reliance on bulky metallic resonators has significantly hindered integration, miniaturization, and extension to lower frequencies. Here, we demonstrate the first on-chip radio-frequency maser operating at room temperature, exploiting optically pumped triplet states of pentacene. The device produces stimulated emission at 106.62 MHz and enables ultra-sensitive microwave magnetic-field detection with a sensitivity of ($\sim 10\,\rm{fT/\sqrt{Hz}}$), functioning simultaneously as a local oscillator and a sensor. By actively controlling microwave dissipation, we achieve efficient regulation of the maser output, revealing a key mechanism for tuning emission in open cavity-free systems. This work extends pentacene-based masers into the radio-frequency regime and establishes a highly integrated on-chip architecture for room-temperature masers, offering a new pathway toward portable quantum devices.

quant-pharXiv:2607.21002•Jul 24, 2026•0 citations
Molecular materials that enable coherent control over an electron's spin state at room temperature are promising candidates for quantum technologies, including quantum sensors and ultra-low noise microwave amplifiers, known as masers. Host-guest molecular crystals enable independent control of spin-active guests and their local environments to enhance molecular spin properties and so improve device performance. Using electron paramagnetic resonance and optically-detected magnetic resonance, we demonstrate the ability to tune triplet population, depopulation, and spin-lattice relaxation by modulating host-dependent lattice rigidity and vibrational coupling to significantly reduce the operating requirements for building useful masers. Importantly, the most rigid host, picene, reveals the ability to slow spin-lattice relaxation without lengthening triplet lifetime, though at the cost of strain-induced line width broadening and reduced triplet spin polarisation. We also find that deuteration reduces the triplet resonance line width and vibrationally-mediated triplet depopulation. Consequently, we find that perdeuterated pentacene in perdeuterated p-terphenyl is the most viable candidate for building a continuous wave maser. This work demonstrates host-guest engineering as an important and practical method for tuning the spin-dependent performance of room-temperature molecular quantum technologies.
Quantum sensing increasingly demands materials combining room-temperature optical spin addressability and coherent control with rapid, accessible fabrication. Yet semiconductor platforms require costly materials and specialized processing, while molecular systems often depend on bespoke synthesis or involved crystal growth. Here we apply microspacing in-air sublimation (MAS) to rapidly fabricate quantum-sensing materials within minutes. Microgram quantities of commercially available precursors crystallize on glass, in air and without vacuum or inert-gas handling. Monitored in situ, growth yields optically clear, stoichiometric single crystals of excellent quality, including plates and needles with intrinsic optical waveguiding. Donor-acceptor charge-transfer co-crystals pairing anthracene or biphenyl with tetracyanobenzene, together with localized-exciton pentacene:pentacenequinone (P:PQ), exhibit room-temperature optically detected magnetic resonance (ODMR). Charge-transfer ODMR resonances reach linewidths below 4MHz4\mathrm{MHz}4MHz, consistent with motional narrowing of mobile triplet excitons, while P:PQ supports coherent ensemble spin control with T2=0.56μsT_2=0.56μ\mathrm{s}T2​=0.56μs. Functionality across chemically and electronically distinct pairs establishes MAS as an accessible screen for molecular quantum-sensing materials, connecting molecular crystal engineering with low-cost, chemically tunable thin triplet-spin layers and waveguiding sensor geometries for quantum sensing and microscopy.
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.
Optically readable molecular spins are attractive as quantum sensors due to their nanoscale modularity, synthetic tunability, and scope for sensitive readout. In particular, photoexcited spin-triplet states in organic molecules are appealing in supporting high optical-spin contrast at room temperature. Their utility is underpinned by their coherence, which warrants a detailed understanding of it. Here, from first principles, we systematically explore the Hahn-echo decoherence of the benchmark molecular system for room-temperature optically detected spin coherence---pentacene guest molecules coupled to a para-terphenyl host. Using generalized cluster-correlation expansion methods, we investigate the mechanisms of nuclear-spin-induced decoherence from zero to high magnetic field, exploring the role of guest vs host molecules, specific nuclei, zero-field splitting interactions, and hyperfine parameters. We describe how zero-field decoherence is driven by ~6 nuclei on the guest, while high-field decoherence is driven by ~600 nuclei in the host; how the longitudinal zero-field splitting parameter, DDD, can prolong T2T_2T2​; and the magnetic-field-dependent processes which drive decoherence. These results advance our understanding of decoherence in optically readable molecular spins, providing insight for their synthetic enhancement and deployment as quantum probes.
Maximizing the number of addressable spins within a fixed volume can improve ensemble quantum sensor sensitivity, but dense packing usually increases dipolar interactions and excited-state transport, shortening coherence and suppressing optical readout. Here we report a 2:1 cocrystal of 6,13-dihydropentacene and pentacene (DHP/Pc) containing 33.3 mol% pentacene (3.3×1053.3\times10^{5}3.3×105 ppm; 9.51×10209.51\times10^{20}9.51×1020 cm−3^{-3}−3), a volumetric spin-site density more than two orders of magnitude above previous benchmarks, NV-diamond and pentacene-doped p-terphenyl (PDP). Despite this density, DHP/Pc exhibits microsecond spin coherence, room-temperature optically detected magnetic resonance and coherent control. Time-resolved measurements indicate that the long-lived triplet population is generated predominantly by intersystem crossing and exhibits strong, non-thermal sublevel polarization. Density-functional theory calculations further suggest that the native cocrystal geometry weakens electronic coupling between neighboring pentacenes, while the higher DHP triplet energy creates a barrier to triplet migration. These results identify molecular packing and coformer triplet energetics as complementary design parameters for preserving coherence in high spin-site density systems, demonstrating cocrystallization as a promising route to dense, optically addressable spin materials for room-temperature ensemble quantum sensing.
We explore an approach for optically pumping a body of optically dense magnetic material. This challenge arises in time-resolved electron paramagnetic resonance (TREPR), triplet-based dynamic nuclear polarisation (DNP), and cavity QED. Crystals of pentacene-doped p-terphenyl were grown around variously shaped ends of optical waveguides, through which pump light could be injected deeply into the crystal. When incorporated into a maser as the gain medium, we found that, compared to conventional side-pumping, 11 times less pump beam intensity was needed to reach the masing threshold and 54 times more pulse energy could be absorbed by the gain medium without damage, resulting in a record peak output power of -5 dBm.
Room-temperature solid-state masers offer exceptional frequency selectivity and ultra-low noise for weak-signal detection. However, their reliance on bulky metallic resonators has significantly hindered integration, miniaturization, and extension to lower frequencies. Here, we demonstrate the first on-chip radio-frequency maser operating at room temperature, exploiting optically pumped triplet states of pentacene. The device produces stimulated emission at 106.62 MHz and enables ultra-sensitive microwave magnetic-field detection with a sensitivity of (∼10 fT/Hz\sim 10\,\rm{fT/\sqrt{Hz}}∼10fT/Hz​), functioning simultaneously as a local oscillator and a sensor. By actively controlling microwave dissipation, we achieve efficient regulation of the maser output, revealing a key mechanism for tuning emission in open cavity-free systems. This work extends pentacene-based masers into the radio-frequency regime and establishes a highly integrated on-chip architecture for room-temperature masers, offering a new pathway toward portable quantum devices.