IIT Roorkee, 2 September 2026: A Fluorescent-Protein Spin Qubit Six to Eight Orders Short of Neural Nitric Oxide
Quentir Medicine Monitor
Evidence-based insights for quantum medicine.
An individual nitric oxide molecule diffuses about two nanometers in roughly 0.2 nanoseconds, which makes the signal close to its point of production exceptionally transient. The methods available today each miss that measurement in a different way: a microelectrode cannot be placed with nanometer precision, a small-molecule indicator disturbs the redox chemistry it is there to report, and neither reads the radical's own magnetism. On 2 September 2026 five researchers at three Indian institutes published the calculation that says how far one new class of protein sensor sits from doing that job.
The preprint, posted to arXiv as 2609.02792 by Parul Raghuvanshi, Sagnik Ganguly, Sharika E, Mohana Priya T. and Vishvendra S. Poonia of IIT Roorkee, IIEST Shibpur and IIT (ISM) Dhanbad, works out the detection limit for spin relaxometry with the fluorescent-protein spin qubit. Their verdict on the sensor as it exists today is that it misses physiological concentrations of nitric oxide by six to eight orders of magnitude. The bottleneck they identify is the qubit's own relaxation time, which is set by the vibrations of the protein that houses it.
What Feder and colleagues published in Nature on 20 August 2025: a spin-1 qubit inside enhanced yellow fluorescent protein
The object this calculation is about was demonstrated last year. Jacob Feder, Benjamin Soloway and their co-authors reported in Nature 645, 73 (2025) that enhanced yellow fluorescent protein hosts an optically addressable spin-1 qubit in the metastable triplet state of its chromophore. The qubit is initialized by 488 nanometer light through spin-selective intersystem crossing, driven by microwaves, and read out through optically activated delayed fluorescence, in which a 912 nanometer pulse lifts the triplet through a higher triplet state back into the singlet manifold. The delayed light that comes back is separated in time from prompt autofluorescence, so the emission carries the spin state.
Its Hamiltonian is a spin-1 with zero-field splitting, measured at D of 2.356 gigahertz and E of 0.458 gigahertz, which puts three zero-field magnetic resonance lines at roughly 0.92, 1.90 and 2.81 gigahertz. The property that matters for medicine is not spectroscopic. Because the sensor is a protein, a cell can be instructed to build it, and it can be fused to a chosen partner protein. That places the sensor spin within the three-nanometer barrel of an enzyme that makes the very radical one wants to measure. This Monitor read the wider case for cells that grow their own quantum sensors on 26 August 2026; the paper now under discussion is the first hard test of whether the idea survives contact with numbers.