Solid-state spin dynamics of a molecular qubit of Ce³

A Ce³⁺ ion is the qubit of a molecular coordination compound with a [ErCeEr] core that was reported as a platform for the implementation of the three qubit (TQC) repetition code for quantum error correction, by exploiting its interaction with two Er³⁺ ancillary qubits. We report here a detailed study of the spin dynamics of this Ce³⁺ qubit by embedding it within [LuCeLu] derivatives of a molecular analogue of the error protected qubit. In these novel molecules the magnetic influence of the Er³⁺ ancillary qubits is suppressed by replacing them with diamagnetic Lu³⁺ ions. The pure site-selective heterometallic nature of these molecules is demonstrated and their magnetization dynamics is studied with SQUID measurements. Most notably, the spin dynamics of the qubits are investigated with X-band pulsed EPR in the solid state and their quantum coherence thus quantified. This is achieved by doping molecules of the qubit within an isostructural diamagnetic crystal lattice made of the [LuLaLu] analogue. The solid solution is accessed by co-crystallization of two different [LnLn'Ln] molecules. Their required stability in solution is here unambiguously demonstrated by paramagnetic ¹H NMR and mass spectrometry. The influence of the ligand scaffold around the [LuCeLu] metal core on the quantum coherence of the Ce³⁺ center is discussed.