On-Chip Magnetic Spectroscopy of a Molecular Spin Clock Transition in Competition with Spin-Spin Interactions

We report a “spin clock transition” between the ground and first excited spin superposition states of a mononuclear Ni(II) molecular complex, [Ni(2-Imdipa)(NCS)](NCS), showing a characteristic non-linear magnetic field dependence that can be directly monitored by on-chip broadband transmission experiments. The sizeable quantum tunnelling splitting in this molecular system, with an <i>S</i> = 1 ground multiplet and strong anisotropy, provides a realization of the simplest non-Kramers system (integer spin). Lowering the temperature of the system down to the millikelvin regime in a dilution refrigerator allows exploring the competition between the onset of antiferromagnetic interactions and the energy gap of the spin clock transition in a fully concentrated sample. In addition, we show the coupling of the spin clock transition to lumped-element superconducting resonators, reaching very high cooperativity values. These results open the possibility of studying the interplay between long-range correlations and photon mediated interactions in a hybrid quantum platform.