Quantum-Projection-Noise-Limited Readout in a Dense NV Ensemble at Room Temperature

Nitrogen-vacancy (NV) centers in diamond provide a robust platform for quantum sensing at room temperature. In dense ensembles, dipole interactions can generate metrologically advantageous entangled states, enabling sensitivity beyond the standard quantum limit (SQL). However, achieving high-fidelity spin-state readout in such systems under ambient conditions remains a challenge, as conventional fluorescence-based detection yields fidelities of only a few percent. Here, we demonstrate a quantum-projection-noise-limited readout of the spin state in a dense NV system at room temperature via the repetitive readout technique [1, 2]. This method utilizes the nitrogen nuclear spin as a quantum memory to enable ancilla-assisted quantum non-demolition measurements of the electronic spin state. Our results indicate that photon shot noise in the NV ensemble is suppressed to the level of quantum projection noise, marking a key advancement toward beyond-SQL quantum sensing.



[1] L. Jiang, J. S. Hodges, J. R. Maze, P. Maurer, J. M. Taylor, D. G. Cory, P. R. Hemmer, R. L. Walsworth, A. Yacoby, A. S. Zibrov, and M. D. Lukin, Science 326, 267 (2009).

[2] N. Arunkumar, K. S. Olsson, J. T. Oon, C. Hart, D. B. Bucher, D. Glenn, M. D. Lukin, H. Park, D. Ham, and R. L. Walsworth, Phys. Rev. Lett. 131, 100801 (2023).