Glasgow researchers report optical spin readout inside porous crystals

University of Glasgow researchers and international collaborators have used light to read electron spins inside a porous crystal at Glasgow’s Advanced Research Center, according to a university announcement published on October 9. The laboratory advance could help researchers develop chemical sensors by combining optical readout with a material that can admit target molecules.

The team describes the result as the first optical measurement of spin resonance inside this class of material, known as a metal-organic framework, or MOF. That priority claim belongs to the researchers. Their announcement describes a step toward sensing, rather than a working instrument that identifies chemicals.

How light reads spins inside a porous framework

In the University of Glasgow announcement carried by Phys.org, Sam Bayliss describes MOFs as rigid, porous molecular scaffolds. Colleagues at the University of Tokyo synthesized the frameworks, while the Glasgow researchers used light to read the magnetic state of spins held inside one of them.

The method is called optically detected magnetic resonance, or ODMR. It detects electron-spin resonance through light and has attracted interest as a way to read spin qubits for quantum sensing. Here, the reported achievement is making that optical readout possible within the porous framework.

Bayliss and Alistair Inglis, of Glasgow’s James Watt School of Engineering, led the university’s contribution. The collaboration also included the universities of Tokyo, Sheffield, Kobe and Saitama, alongside JEOL Ltd. and the Institute for Molecular Science.

Why porous crystals interest quantum-sensor researchers

The university contrasts molecular spins with those found in defects in crystals, such as diamond nitrogen-vacancy centers, an established example of optically detectable spins. Molecular structures can be designed chemically, allowing researchers to adjust their spin properties. MOFs also offer control over where spins sit and how they are oriented.

Their pores provide another potential advantage: target substances can enter the scaffold and approach the spins. Inglis says spin resonance carries information about molecules and their environment. Interactions at close range could therefore provide a route to detecting substances held within the framework.

Loading target molecules into the scaffold and reading them through the optical technique remains a proposed use in this announcement. The report does not demonstrate chemical identification with the new optical readout or establish which substances it could distinguish, at what concentrations or with what reliability.

Earlier MOF research already measured lithium ions

Chemical quantum sensing with MOFs predates the new announcement. A 2022 study by Lei Sun and colleagues, published online in the Journal of the American Chemical Society on October 6 that year, demonstrated room-temperature sensing of lithium ions in solution using organic radicals incorporated into a microporous framework.

Those researchers reported room-temperature electron-spin coherence and microwave addressability. They identified lithium and measured its concentration using electron paramagnetic resonance methods. The framework’s high surface area, they reported, gave the lithium analytes access to the organic qubits.

The earlier experiment provides relevant precedent, but it used a different readout approach and does not validate the new optical result. The distinction is the advance being claimed: optical access to spins within a framework, rather than the first use of any MOF for chemical quantum sensing.

Practical temperatures and stronger signals come next

Inglis identified two immediate priorities: “The next step is pushing this to work at more practical temperatures and tuning the chemistry to make the signal stronger.” The announcement does not specify the new experiment’s operating temperature or establish when those improvements might be achieved.

The team also proposes a longer-term possibility: a collection of differently designed MOFs, each responding differently to chemicals. Their combined response patterns might identify substances as a “quantum nose.” That is a proposed sensing architecture, not an announced working device.

The new research is identified as Miku Inoue and colleagues’ “Optically Addressable Spins in a Metal–Organic Framework,” in the Journal of the American Chemical Society. October 9 dates the university report; it does not establish when the experiment occurred or the paper’s exact publication date.

For researchers developing molecular sensors, the immediate result is another way to access spins in a chemically adjustable material. Detection limits, chemical selectivity, repeatability and practical operating temperatures remain unestablished by the announcement, which gives no commercial deployment date or demonstrated benefit for end users.