Abstract
<jats:p>Quantum sensors harnessing multi-quantum coherence offer a promising route to precision metrology beyond the standard quantum limit. Although molecular spin qudits provide engineerable high-dimensional Hilbert spaces, the rapid decoherence of high-order spin states typically restricts their operation to cryogenic environments. Here, we synthesize a high-spin molecular magnet N@C60-C9H8O (electron spin S = 3/2), via a single-step gas-phase ion implantation technique. Leveraging its ultralong room-temperature coherence time (~38 μs), N@C60-C9H8O achieves an AC magnetic sensing sensitivity of 4⋅10-8 T Hz-1/2. Based on full coherent control over the four-level electron spin manifold, we demonstrate the sensing enhancement beyond the standard quantum limit utilizing molecular spin cat states at room temperature. These results exhibit the immense application potential of high-spin molecular qudits in ambient quantum metrology.</jats:p>