Signal amplification in a solid-state sensor through asymmetric many-body echo

Electronic spins of nitrogen-vacancy centres in diamond constitute a promising system for micro- and nanoscale magnetic sensing^1-4, because of their operation under ambient conditions⁵, ease of placement in close proximity to sensing targets⁶ and biological compatibility⁷. At high densities, the electronic spins interact through dipolar coupling, which typically limits⁸ but can also potentially enhance⁹ sensing performance. Here we report the experimental demonstration of many-body signal amplification in a solid-state, room-temperature quantum sensor. Our approach uses time-reversed two-axis-twisting interactions, engineered through dynamical control of the quantization axis and Floquet engineering¹⁰ in a two-dimensional ensemble of nitrogen-vacancy centres. We observe that optimal amplification occurs when the backward evolution time equals twice the forward evolution time, in sharp contrast to the conventional Loschmidt echo^11,12. These observations can be understood as resulting from an underlying time-reversed mirror symmetry of the microscopic dynamics, providing key insights into signal amplification and opportunities for practical entanglement-enhanced quantum sensing.