Observation of Cooperative Electronic Quantum Tunneling: Increasing Accessible Nuclear States in a Molecular Qudit

As an extension of two-level quantum bits (qubits), multilevel systems, so-called qudits, where d represents the Hilbert space dimension, have been predicted to reduce the number of iterations in quantum computation algorithms. This has been tested in the well-known [TbPc2]0 SMM, which allowed the implementation of the Grover algorithm in a single molecular unit. In the quest for molecular systems possessing an increased number of accessible nuclear spin states, we explore herein a dimeric Tb2-SMM via single crystal {\mu}-SQUID measurements at sub-Kelvin temperatures. We observe ferromagnetic interactions between the Tb(III) ions and cooperative quantum tunneling of the electronic spins with spin ground state \textit{J} = {\pm}6. The strong hyperfine coupling with the Tb(III) nuclear spins leads to a multitude of spin reversal paths leading to seven strong hyperfine driven tunneling steps in the hysteresis loops. Our results show the possibility to read-out the Tb(III) nuclear spin states via the cooperative tunneling of the electronic spins, making the dimeric Tb2-SMM an excellent nuclear spin qudit candidate with d =16.
Comment: Manuscript contains 17 pages, 4 figures, and SI contains 10 pages and 8 figures