Achieving strain-limited ensemble dephasing times in solid-state quantum sensor with a compact single magnet assembly
Y. MASUYAMA, Chikara Shinei, Haruki Tanaka +5 more
Solid-state quantum sensors offer the promising prospect of high-sensitivity sensing across various environments, including at room temperature and atmospheric pressure. Highly sensitive solid-state quantum sensors require long ensemble dephasing times (T2*) in mm-scale sample areas. This requirement demands a highly uniform bias magnetic field across all qubits, which has traditionally required large magnetic field sources such as Helmholtz coils or a pair of magnets. Meanwhile, to expand the range of applications of quantum sensors, portable sensors are required, but it is difficult to carry these large magnets. Balancing the miniaturization of the quantum sensor with high sensitivity is a significant challenge. In this study, we achieve a long ensemble dephasing time for nitrogen-vacancy (NV) centers in a large sample volume using a single, compact, and optimized magnet assembly. By using a magnet design derived from an inverse problem-based analysis, we reduced the magnet assembly volume to 0.23% of the Helmholtz coil volume. We achieve an ensemble dephasing time of 5.32 μs for the entire NV center ensemble across the sample thickness, comparable to that obtained with a standard Helmholtz coil setup. This dephasing is limited by strain-induced dephasing across the diamond sample thickness, with a dephasing rate of 188 kHz, which represents the state-of-the-art diamond quality for bulk quantum sensors. Our work paves the way for the miniaturization of high-sensitivity quantum sensors, enabling new sensor designs and the construction of compact, highly sensitive quantum sensor arrays.
Applied Physics Letters•Sep 28, 2026•0 citations