13 November 2025
Electrifying Quantum Sensing
Diamond nitrogen-vacancy (NV) centers, already a cornerstone of quantum sensing, can now reveal their spin state electrically, not just optically. By identifying optimal laser wavelengths, researchers at the Walter Schottky Institut have achieved the highest electrically detected spin contrast to date, paving the way for more compact and integrable NV-based quantum devices.
Nitrogen-vacancy (NV) centers in diamond are among the few quantum systems that have already found a way into practical and commercial applications. They are most widely recognized in the field of quantum sensing, where they enable the precise detection of nanoscale magnetic fields in materials and life sciences, as well as the measurement of pressure or temperature under extreme conditions. Beyond sensing, diamond NV centers are also considered promising candidates for room-temperature quantum computing and communication.
Up to now, nearly all NV-based applications rely on an optical readout of the NV centers' spin state by using their spin-dependent emission of red light. Recently, researchers, including Martin Brandt’s group at the Walter Schottky Institut, have demonstrated that the same spin information can also be obtained electrically by detecting the photocurrent generated in the diamond under laser illumination. This new approach offers some straightforward advantages, including enhanced detection efficiency and the potential for further miniaturization and direct integration of NV-based sensors into electronic devices and daily-life applications.
To advance the electrical readout towards robust and practical use, the research group at the Schottky Institut is systematically exploring the optimal conditions and technical requirements for electrical readout. In their recent publication in Applied Physics Letters, “Optical and electrical readout of diamond NV centers in dependence of the excitation wavelength”, they focus on optimizing the laser excitation that induces the spin-dependent photocurrent in diamond.
To generate the charge carriers for the photocurrent, the NV center is ionized and subsequently recharged by the laser light, and thus cycling between two different charge states. While the processing of spin information takes place exclusively in the negative charge state of the NV center, the Brandt group showed that the center spends a substantial amount of time in its neutral state and that the critical step in the generation of photocurrent is the recharging back to the negative state. Consistent with this finding, the group identified several distinct laser wavelengths that can drive resonant transitions within the NV center and significantly enhance the electrical readout. In particular, illumination with light of 575 nm wavelength, corresponding to the energy of the so-called zero-phonon transition in the neutral charge state, produced the highest electrically detected spin contrast published to date.
With these results and other ongoing projects optimizing the diamond host material and its electronic properties, the MCQST group aims to contribute to the development of compact, cost-efficient, and integrable NV quantum sensors.
Publication
Optical and electrical readout of diamond NV centers in dependence of the excitation wavelength
L. M. Todenhagen and M. S. Brandt
Appl. Phys. Lett. 126, 194003 (2025)
DOI: 10.1063/5.0264362
Contact
Lina M. Todenhagen
Doctoral Candidate in NV Team
Walter Schottky Institute
lina.todenhagen[at]wsi.tum.de
Prof. Dr. Martin S. Brandt
Walter Schottky Institute
brandt[at]wsi.tum.de