This polymer-based system shows that coherent quantum behavior can be designed into stable, tunable, solution-processable materials compatible with real devices.
(Nanowerk Spotlight) Quantum technologies promise capabilities that traditional electronics cannot deliver. These include ultrasensitive detection of magnetic fields, radically faster computations, and secure communication networks that are immune to eavesdropping. Yet building such systems outside the lab has proved remarkably difficult.
The problem is not a lack of theoretical understanding or engineering tools. It is that the quantum effects being used are extremely fragile. To keep them stable, researchers often rely on extreme conditions such as ultra-low temperatures, isolated environments, or highly purified crystalline materials.
This dependence on ideal conditions makes many quantum platforms hard to scale and difficult to integrate with real-world technologies. One of the clearest examples is the qubit, the basic unit of quantum information. In solid-state systems, qubits are often created by placing electron spins into precisely controlled environments within materials like diamond or silicon carbide. These spins can store and process quantum information, but they are effectively locked in place. The host materials are rigid, hard to modify, and not easily integrated into larger devices. There is little room for customization, and large-scale deployment remains out of reach.
Molecular systems offer a different approach. Chemists can design them from scratch, tailoring electronic structure, spin behavior, and physical properties with atomic precision. These systems are flexible and chemically tunable in ways that solid-state crystals are not.
However, most known molecular qubits become unstable or lose coherence in solid form. The spins interact with their surroundings in ways that destroy the quantum state. To preserve coherence, researchers have had to embed these systems in frozen solvents or heavily diluted matrices. That keeps them stable, but removes them from any realistic device environment.
The central challenge is to create a material that combines the quantum performance of these molecular systems with the structural and thermal stability needed for real applications. This means achieving coherent spin behavior in the solid state, under ambient conditions, without sacrificing chemical control or processability.
That is what the authors of a new study in Advanced Materials (“Solid‐State Quantum Coherence From a High‐Spin Donor–Acceptor Conjugated Polymer”) have achieved. They report a polymer that supports solid-state quantum coherence at room temperature. Built from an engineered donor and acceptor structure, this conjugated material exhibits long spin lifetimes, coherent manipulation of quantum states, and compatibility with standard device processing. It does so without requiring cryogenics, isolation, or rigid crystallinity. This work introduces a new design framework for quantum materials that is rooted in synthetic chemistry rather than defect engineering.
The material is a conjugated polymer made by alternating electron-rich and electron-poor units along the molecular chain. The donor unit is based on dithienosilole, while the acceptor unit is a thiadiazoloquinoxaline. These two components create an electronic structure in which unpaired electron spins become stabilized along the backbone of the polymer. To make the material soluble and prevent aggregation, the researchers added long hydrocarbon side chains. These chains also help control the conformation of the backbone, maintaining electronic coherence across the molecule.
A central design feature is the use of a silicon atom at the core of the donor unit. This silicon center introduces a small twist into the backbone structure. That twist prevents the chains from stacking too closely together, which would otherwise lead to strong spin interactions and rapid decoherence. At the same time, the twist does not break electronic communication along the chain. The result is a material in which spins are delocalized but not exposed to the most harmful environmental noise.
Synthesis of the high-spin donor–acceptor conjugated polymer and correlation of macromolecular, spin, and topological structure. A) The molecular building blocks and Stille cross-coupling polymerization used to synthesize the polymer that exhibits B) a high-to-low spin energy gap. C) Spin density distribution for the triplet state of the n = 8 oligomer modeled at the (U)DFT/B3LYP/6-31G** level. The blue and green surfaces represent positive and negative contributions of the spin density at an isovalue = 0.02 au. D) Topological structure of the backbone. (Image: Reprinted from DOI:10.1002/adma.202501884, CC BY) (click on image to enlarge)
The researchers confirmed the structure and properties of the polymer using both theory and experiment. Quantum chemical modeling showed that the spin density becomes spread out along the polymer as the chain length increases. At a certain critical length, the material adopts a high-spin ground state, meaning the lowest energy configuration involves two unpaired electrons aligned in the same direction. This is the same type of state that forms the basis of some solid-state qubit systems.
Magnetometry experiments confirmed that the polymer does indeed have a total spin of one, consistent with a triplet ground state. Electron paramagnetic resonance spectroscopy revealed narrow, symmetric signals with a g-factor very close to that of a free electron. This suggests that the material has low spin orbit coupling, which is essential for maintaining coherence. The spins showed only weak interactions with nearby nuclear spins, further reducing sources of decoherence.
The key test was whether the material could support quantum coherence in the solid state. To answer this, the team measured two quantities. The first is the spin lattice relaxation time, or T1, which indicates how long a spin takes to return to equilibrium after being disturbed. The second is the phase memory time, or Tm, which tells how long a spin can remain in a coherent superposition state before becoming randomized by its surroundings.
At room temperature, the polymer exhibited a T1 of about 44 microseconds and a Tm of 0.3 microseconds. These values increased significantly at lower temperatures. At 5.5 kelvin, T1 reached 44 milliseconds and Tm extended to over 1.5 microseconds. These times are longer than those reported for many other synthetic molecular spin systems, including radicals and organometallic complexes. More importantly, they were achieved without embedding the polymer in a frozen matrix or chemically isolating the spins.
The team also demonstrated control over the quantum state of the spins using microwave pulses. They observed Rabi oscillations, a signature of coherent spin manipulation. The frequency of these oscillations scaled with the strength of the applied field, indicating that the spins were being rotated in a predictable and controllable way. These measurements confirm that the system meets the basic criteria for a single-qubit platform.
The structural features of the polymer play a direct role in enabling this behavior. The twist in the backbone introduced by the silicon atom, along with the bulky side chains, prevents stacking and aggregation. This reduces the density of low-energy vibrations that typically couple to electron spins and destroy coherence. The delocalization of the spin over the backbone also spreads out the interaction with nuclear spins, making the system more resistant to decoherence.
The researchers also compared this polymer to a structurally similar version in which the silicon atom was replaced by carbon. The carbon-based polymer showed much shorter relaxation times, suggesting that even small changes in backbone structure can have large effects on quantum performance. This kind of sensitivity highlights the value of molecular design as a tool for engineering spin dynamics.
Beyond coherence, the polymer also shows promise for integration into real devices. It forms uniform thin films from solution and functions as a p-type semiconductor in field-effect transistors. It exhibits modest charge mobility and stable operation under repeated cycling. These properties open the door to device architectures that can combine electronic and spin functionality. One example is electrically detected magnetic resonance, a method for reading out spin states using charge transport rather than optical signals.
The polymer also shows potential for quantum sensing. Its coherent spin states are sensitive to interactions with nearby magnetic nuclei. This sensitivity could be used to detect the presence of specific molecules or to map local environments. Because the material works at room temperature and does not require isolation, it could be used in practical sensing platforms that operate under ambient conditions.
What distinguishes this work is not just that the polymer functions as a qubit material. It is that it does so without the usual constraints of cryogenics, dilution, or rigid ordering. The spins remain coherent in a magnetically dense, amorphous solid. That is a regime where most molecular systems fail. This performance is possible because of the precise control over molecular structure and spin distribution that the polymer design enables.
This work shows that it is possible to combine synthetic tunability with solid-state coherence in a single molecular system. It provides a new platform for exploring spin dynamics and quantum control in organic materials. It also points toward a future in which quantum devices are not limited to carefully isolated crystals but can be built from flexible, processable, and chemically diverse macromolecules.
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