Molecule Enables High-Precision Quantum Sensing

A new quantum sensing method from the University of Waterloo could make it possible to measure the magnetic fingerprints of single protein structures and other biomolecules—an advance with far-reaching implications for drug discovery and structural biology.

The approach, developed by researchers at the Institute for Quantum Computing (IQC), turns a single molecule into a quantum sensor. Quantum sensors exploit quantum properties to achieve precision that conventional instruments struggle to match, and this work reports a demonstration that has not been achieved before.

At the heart of the technique is sensitivity to the spin and local magnetic environment of nearby atoms. Because each atom’s nuclear spins generate distinct resonance conditions, the presence of nearby nuclei shifts how the sensor evolves in time. In effect, the sensor “reads” molecular-scale magnetic structure rather than relying on optical contrast alone.

Instead of using the widely adopted route of synthetic diamonds with light-based readout, the team uses a molecular quantum system called trityl-OX063. The sensor’s spin is isolated and protected to preserve coherence, allowing the quantum state to survive long enough for measurement.

The readout is mechanical: the electron spin of OX063 responds to fluctuations in magnetic fields created by nearby nuclear spins, and the resulting signal is detected with nanoscale force probes. These nanowire probes are about 100 nanometers across—roughly the scale of a virus—and extend to around 20 microns, enabling detection close to the sensing site.

A major technical milestone was maintaining coherence. The researchers introduced a control sequence that extended the coherence time to 400 microseconds, about sixty times longer than standard spin-echo performance in the same setup.

With the improved stability, the sensor can already detect magnetic states from roughly ten spins. The team notes that reaching true single-spin sensitivity is a key step toward mapping how individual molecules are arranged and interacting.

Unlike many existing molecular imaging workflows that require larger samples and therefore blur unique structural details, this quantum approach targets the spin-level information that is directly tied to molecular identity and arrangement.

The study, titled “Long-Lived Mechanically Detected Molecular Spins for Quantum Sensing,” appears in Physical Review X and signals a new paradigm in nanoscale quantum measurement, bringing viral-scale excitement to a field racing toward single-molecule structural mapping.