Diamonds have long captivated scientists not only for their extraordinary hardness and optical clarity but also for their hidden potential as platforms for quantum technologies. Central to this promise are defects embedded within the diamond lattice known as nitrogen vacancy (NV) centres. These atom-sized color centers have become indispensable in the quest for quantum sensing and quantum computing, owing to their unique electron spin properties that can be precisely controlled and read out. Yet, despite significant advances, a critical bottleneck has persisted: accurately and efficiently reading out the spin state of individual NV centres under ambient conditions. A groundbreaking study from the Helmholtz-Zentrum Berlin (HZB) now promises to revolutionize this challenge by introducing a novel electrical readout mechanism for NV spin states, offering a pathway towards compact, scalable quantum sensors and devices.
Traditionally, the state of the electron spin in NV centres is interrogated optically. When illuminated with green laser light, NV centers fluoresce, emitting photons whose properties correlate with the underlying spin configuration. Detecting these spin-dependent photons, however, is notoriously difficult. The inherently weak single-photon emission from a single NV centre demands sophisticated optical setups and ultra-sensitive detectors. Such arrangements are not only bulky but also sensitive to environmental noise and challenging to miniaturize. For quantum technologies to transcend laboratory demonstrations and find real-world applications, alternative readout methods that bypass these constraints are desperately needed.
The innovative approach developed by the HZB team artfully circumvents these optical limitations by exploiting an inherently electrical signature linked to the NV centre’s spin state. The key insight stems from recognizing that NV centres, beyond their spin, also possess an associated electrical charge. When excited by a green laser, electron-hole pairs are generated in the diamond, leading to free charge carriers. These charges interact with surface states, creating measurable changes in the local electric potential. By employing an advanced variant of atomic force microscopy known as Kelvin probe force microscopy (KPFM), the researchers were able to spatially resolve these potential differences with nanometer precision, effectively mapping the electrical landscape induced by individual NV centres.
This electrical detection method hinges on the dependence of the generated photovoltage on the spin state of the NV centre. As the NV electron spin undergoes coherent manipulation via microwave excitation, the local charge environment — and hence the photovoltage detected by the KPFM tip — responds accordingly. By tunably driving the spin resonance and simultaneously recording the spatially-resolved photovoltage, the researchers succeeded in directly reading out single-spin dynamics without relying on photon detection. This elegant strategy not only increases the signal strength compared to weak fluorescence but also significantly reduces experimental complexity.
Capturing the spin dynamics electrically through photovoltage paves the way for a fundamentally new type of quantum sensor. The readout technique is inherently more robust and compact since it omits the need for bulky optics, single-photon detectors, or complicated cryogenic setups typically required for high-fidelity spin detection. Instead, simple electrical contacts suffice, drastically shrinking the device footprint while enhancing integration potential with existing electronic architectures. The method’s sensitivity to local spin states at the nanoscale heralds advances in magnetic field sensing, nanoscale thermometry, and pressure measurements pertinent to quantum metrology.
Moreover, the ability to manipulate and detect spin coherence electrically under ambient conditions — without the need for vacuum or low temperatures — is vital for real-world implementation of diamond quantum technologies. The photovoltage change linked to spin transitions was not only observed statically but also recorded dynamically, demonstrating coherent control of spin states in time-resolved fashion. This breakthrough reveals that spin qubits in diamond can be addressed and read out fully electrically with high spatial resolution, opening novel avenues in scalable quantum information processing and spintronics.
The implications extend beyond diamond NV centres alone. Many other solid-state systems with electron spin defects, such as silicon carbide or rare-earth doped crystals, also exhibit spin-dependent charge dynamics that could be harnessed using this electrical detection scheme. By generalizing these principles, a broader class of quantum materials and devices might benefit from simplified spin readout protocols, accelerating the development of quantum computing components, spin-based sensors, and hybrid quantum-electronic platforms.
Fundamental physics also stands to gain. Mapping photovoltage signals with nanometer precision provides insight into charge-spin interactions at surfaces and interfaces, shedding light on spin-dependent charge transport phenomena. This can deepen understanding of decoherence mechanisms that limit quantum device performance and guide the engineering of tailored quantum materials with optimized spin coherence times. The research thereby bridges basic science and application-driven engineering, fostering both.
Looking forward, the HZB team envisages the integration of this photovoltage readout technique into on-chip devices composed of nanoscale diamond elements with built-in microwave and electrical contacts. Such miniaturized diamond-based quantum sensors could monitor magnetic or electric fields with unprecedented spatial resolution and compactness, suitable for portable medical diagnostics, environmental monitoring, or fundamental research. This elegant electrical approach may thus accelerate the commercialization of quantum technologies, making them practical and cost-effective.
The study represents a pivotal leap toward the vision of scalable, electrically controlled quantum systems that operate under everyday conditions. It addresses a longtime technological hurdle by substituting complex photon counting with an all-electrical interface, merging the extraordinary physical properties of diamond NV centres with powerful scanning probe microscopy. This interdisciplinary advance highlights the synergy of optics, electronics, and quantum physics in propelling next-generation quantum device engineering.
In summary, through the innovative use of photo-induced voltages detected by Kelvin probe force microscopy, the HZB research team has demonstrated an unprecedented method for single-spin readout in diamond at room temperature. By leveraging electrical signals tightly coupled to spin states, the work alleviates the need for intricate optical setups, enabling compact and robust quantum sensors and potentially revolutionizing quantum information science. This breakthrough transforms the landscape of quantum measurement technologies and creates new pathways for their real-world deployment.
Subject of Research:
Not applicable
Article Title:
Voltage detected single spin dynamics in diamond at ambient conditions
News Publication Date:
14-Apr-2025
Web References:
http://dx.doi.org/10.1038/s41467-025-58635-3
Image Credits:
Credit: Martin Künsting / HZB
Keywords:
Spin manipulation, Sensors, Quantum information science, Signaling complexes, Qubits, Atomic force microscopy
