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Long-Lived Mechanically Detected Molecular Spins for Quantum Sensing

Sahand Tabatabaei, Pritam Priyadarsi, Daniel Tay, Namanish Singh, Pardis Sahafi, Andrew Jordan, and Raffi Budakian*

  • *Contact author: rbudakian@uwaterloo.ca
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Phys. Rev. X 16, 031018 – Published 27 July, 2026

DOI: https://doi.org/10.1103/c994-bzx7

Abstract

Quantum sensors based on individual spins provide unprecedented access to local magnetic fields in condensed matter, chemistry, and biology, with solid-state defect spins emerging as the leading platform. However, their molecular-sensing capabilities are limited by confinement to a host lattice, which prevents placement in close proximity to a target molecule. Molecular spins offer an alternative, enabling chemical tunability and flexible positioning relative to the target system. Here we present a nanoscale sensing platform that combines molecular electron spins, ultrasensitive mechanical readout, and Hamiltonian engineering. Using a modified XYXY dipolar decoupling sequence, we suppress electron-electron dipolar interactions across a broad distribution of control fields, extending coherence times to ∼400  μs in an attoliter-scale droplet containing ∼100 trityl-OX063 radicals. Leveraging this sequence, we demonstrate frequency-selective detection of nanotesla-scale ac fields and perform sensing and spectroscopy of small, local nuclear-spin ensembles. Collectively, these results establish spin-based quantum integrated nanomechanical transduction as a framework for quantum sensing that affords molecular-level control over sensor properties and enables direct integration into complex molecular targets.

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Quantum sensors based on solid-state defect spins are inherently limited by their host crystal lattices, which prevents flexible placement within nanometers of target molecules. We overcome this restriction by establishing a nanoscale sensing platform that integrates chemically adaptable molecular electron spins with ultrasensitive mechanical readout and a tailored pulse sequence that rescales dipolar interactions. Using this architecture, we successfully extend spin coherence times up to hundreds of microseconds in an attoliter-scale droplet. Our approach enables frequency-selective detection of nanotesla-scale alternating fields and resolves the local magnetic spectra of nearby nuclear spins. By demonstrating molecular-level control over sensor properties, we pave the way for spatially resolved magnetic resonance imaging directly integrated within complex biological and chemical targets.

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Phys. Rev. X 16, 031018– Published 27 July, 2026
  • Received 6 March 2026
  • Revised 18 May 2026
  • Accepted 1 June 2026
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