In a remarkable leap forward for quantum technology, researchers at Delft University of Technology have, for the first time, directly observed the nuclear spin of a single atom flipping between discrete quantum states in real time. This breakthrough, accomplished using a scanning tunneling microscope (STM), opens up new horizons in the precise control and measurement of atomic-scale magnetic phenomena. Their findings, published in Nature Communications, demonstrate an unprecedented ability to “read out” the magnetic orientation of the nucleus via the electron cloud surrounding it, a process that holds immense promise for quantum sensing and information technologies.
The scanning tunneling microscope stands at the heart of this achievement. With its atomically-sharp metallic needle, the STM can resolve individual atoms on surfaces by detecting currents generated from electrons tunneling between the tip and the sample. However, while it has been known that STM can sense electron spin states, directly accessing nuclear spins has posed a formidable challenge due to their relatively weak magnetic moments and the indirect nature of their interactions with the electrons. The Delft team ingeniously exploited the subtle hyperfine interactions—delicate quantum couplings between the nucleus and electron spins—to infer nuclear spin orientations by observing changes in the tunneling current.
Electron spins in atoms typically fluctuate on extremely short timescales, often mere nanoseconds, making real-time detection and control difficult. Nuclear spins, by contrast, can be far more stable, but their weak signals have long eluded rapid measurement. Surprisingly, the researchers found that the nuclear spin of the targeted atom remained stable for several seconds before flipping states. This timescale, orders of magnitude longer than electron spin lifetimes, allowed the team to monitor the nuclear spin transitions live on their computer screens, truly witnessing quantum behavior unfold in real time.
The real novelty of the experiment lies in the concept of single-shot readout—rapidly and reliably determining the nuclear spin state from a single measurement without averaging over multiple trials. Previous techniques often required repeated measurements to infer nuclear spin behavior, because the signal-to-noise level was prohibitively low or the measurement process itself disturbed the spin state. By tuning the STM setup and leveraging the hyperfine interaction, the Delft scientists detected fluctuations in the tunneling current that directly corresponded to the nuclear spin flipping between two distinct quantum states. This capability not only advances fundamental quantum measurement techniques but sets the stage for future quantum control schemes, where nuclear spins can serve as qubits or sensors.
This work reveals that nuclear spins, despite their small magnetic moment, have lifetimes suitable for quantum information tasks. While electron spins decohere within nanoseconds under typical conditions, nuclear spins act as robust quantum memories, persisting for seconds or longer. Capturing their dynamics on such timescales with an STM—an instrument traditionally used for imaging surfaces—reveals unprecedented atomic-scale information and control, which was previously thought impossible.
The implications for quantum sensing are profound. Nuclear spins tethered to surface atoms can function as ultra-sensitive probes of magnetic and electric fields, chemical environments, or even mechanical strains, all at the atomic scale. This capability surpasses traditional macroscopic sensors, promising advances in nanoscale materials science, condensed matter physics, and even the detection of elusive phenomena such as dark matter or novel quantum phases.
Achieving this feat required overcoming several technical hurdles. The STM tip must be exquisitely stable and sensitive to detect the minute current variations caused by nuclear spin flips, all while avoiding perturbation of the spin state. The research team employed rapid measurement protocols, coupled with sophisticated data analysis, to distinguish genuine nuclear spin signals from noise and other electronic fluctuations. Their success paves the way for the development of STM-based quantum sensors that can operate as scalable platforms for quantum simulation or computing.
The interplay of electron and nuclear spins within a single atom, long studied theoretically, now finds concrete expression through this experiment. The so-called hyperfine interaction, a quantum mechanical coupling arising from contact and dipolar effects between the electron cloud and the atomic nucleus, acts as the conduit transmitting nuclear spin information to the electron states detectable by STM. By harnessing this subtle yet fundamental interaction, researchers can now observe and manipulate nuclear spins with unprecedented precision.
Looking ahead, the researchers envision leveraging single-shot nuclear spin readout for quantum state preparation and error correction protocols, essential for robust quantum computing. On a practical level, this capability could enable the design of novel quantum devices where nuclear spins serve as stable information storage nodes or sensors integrated directly at the atomic scale. Furthermore, the experimental framework provides a testbed for exploring quantum coherence, decoherence mechanisms, and spin dynamics in complex materials.
This landmark study, conducted under the lead of Professor Sander Otte, marks a crucial step in the frontier of quantum measurement science. By illuminating the “silent” spins of atomic nuclei, the Delft team has expanded our toolkit for probing and harnessing the quantum world. As the field progresses, such techniques promise to transform our understanding of matter and underpin next-generation quantum technologies.
In summary, this research not only captures a fundamental quantum phenomenon—nuclear spin flips—in real time but also establishes STM as a versatile platform for quantum sensing and manipulation at the atomic scale. The ability to observe and control nuclear spins with such fidelity offers exciting possibilities in physics, materials science, and quantum engineering. As quantum technology races forward, these findings stand as a testament to the ingenuity and precision now achievable in experimental quantum science.
Subject of Research: Not applicable
Article Title: Single-shot readout of the nuclear spin of an on-surface atom
News Publication Date: 21-Aug-2025
Web References: https://www.nature.com/articles/s41467-025-63232-5
References: DOI: 10.5281/zenodo.15518772
Image Credits: Scixel
Keywords
Nuclear spin, quantum spin flipping, scanning tunneling microscope, single-shot readout, hyperfine interaction, quantum measurement, atomic scale sensing, quantum sensing, quantum information, electron spin, decoherence, quantum simulation
