Vibronic Relaxation Pathways in Molecular Spin Qubit Na₉[Ho(W₅O₁₈)₂]·35H₂O under Pressure

In order to explore how spectral sparsity and vibronic decoherence pathways can be controlled in a model qubit system with atomic clock transitions, we combined diamond anvil cell techniques with synchrotron-based far infrared spectroscopy and first-principles calculations to reveal the vibrational response of Na (Formula presented.) [Ho(W (Formula presented.) O (Formula presented.)) (Formula presented.)]·35H (Formula presented.) O under compression. Because the hole in the phonon density of states acts to reduce the overlap between the phonons and f manifold excitations in this system, we postulated that pressure might move the HoO (Formula presented.) rocking, bending, and asymmetric stretching modes that couple with the (Formula presented.) = ±5, ±2, and ±7 levels out of resonance, reducing their interactions and minimizing decoherence processes, while a potentially beneficial strategy for some molecular qubits, pressure slightly hardens the phonons in Na (Formula presented.) [Ho(W (Formula presented.) O (Formula presented.)) (Formula presented.)]·35H (Formula presented.) O and systematically fills in the transparency window in the phonon response. The net result is that the vibrational spectrum becomes less sparse and the overlap with the various (Formula presented.) levels of the Ho (Formula presented.) ion actually increases. These findings suggest that negative pressure, achieved using chemical means or elongational strain, could further open the transparency window in this rare earth-containing spin qubit system, thus paving the way for the use of device surfaces and interface elongational/compressive strains to better manage decoherence pathways.