Detecting Individual Nuclear Spins
For researchers pursuing qubits, magnetic sensors, and other applications of nuclear spins, erbium-doped yttrium orthosilicate (Er:YSO) is an attractive solid-state platform. Now, thanks to new work by Andreas Reiserer of the Technical University of Munich and his collaborators, those applications are a step closer to realization. The researchers demonstrated that they could distinguish five different yttrium nuclei that surrounded a single erbium nucleus in a thin membrane of Er:YSO [1]. In future applications, the procedure could potentially be extended to address each yttrium spin individually.
Several factors account for the appeal of Er:YSO. Erbium has an optical transition that is extremely narrow and couples magnetically to neighboring Y spins, which split the transition frequency. Because the coupling depends on the relative orientations of the spins and the applied magnetic field, the splitting engendered by each yttrium spin is different. Unfortunately, the shift is hard to detect because the optical transition is faint. Increasing the concentration of erbium dopants would boost the signal but at the cost of blurring the individual splittings such that they cannot be recognized.
Reiserer and his collaborators hit on another way to boost the signal. They fashioned thin membranes of YSO doped with trace amounts of erbium and placed them in a type of optical cavity known as a Fabry-Perot resonator. Thanks to the resonator’s quality factor of almost 107, the signal from a single erbium dopant was enhanced by a factor of 100. When the researchers swept through the magnetic field, they found distinct signals originating from five of the erbium dopant’s closest neighbors.
–Charles Day
Charles Day is a Senior Editor for Physics Magazine.
References
- A. Ulanowski et al., “Cavity-enhanced spectroscopy of individual nuclear spins in a dense bath,” PRX Quantum 6, 020344 (2025).