10.1021/acscentsci.5b00338.s001 Joseph M. Zadrozny Joseph M. Zadrozny Jens Niklas Jens Niklas Oleg G. Poluektov Oleg G. Poluektov Danna E. Freedman Danna E. Freedman Millisecond Coherence Time in a Tunable Molecular Electronic Spin Qubit American Chemical Society 2015 Transition metal complexes offer EPR QIP CS 2 solubility T 2 Tunable Molecular Electronic Spin Qubit Quantum information processing Millisecond Coherence Time Ph 4 P qubit design principles 2015-12-23 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Millisecond_Coherence_Time_in_a_Tunable_Molecular_Electronic_Spin_Qubit/2006931 Quantum information processing (QIP) could revolutionize areas ranging from chemical modeling to cryptography. One key figure of merit for the smallest unit for QIP, the qubit, is the coherence time (<i>T</i><sub>2</sub>), which establishes the lifetime for the qubit. Transition metal complexes offer tremendous potential as tunable qubits, yet their development is hampered by the absence of synthetic design principles to achieve a long <i>T</i><sub>2</sub>. We harnessed molecular design to create a series of qubits, (Ph<sub>4</sub>P)<sub>2</sub>[V­(C<sub>8</sub>S<sub>8</sub>)<sub>3</sub>] (<b>1</b>), (Ph<sub>4</sub>P)<sub>2</sub>[V­(β-C<sub>3</sub>S<sub>5</sub>)<sub>3</sub>] (<b>2</b>), (Ph<sub>4</sub>P)<sub>2</sub>[V­(α-C<sub>3</sub>S<sub>5</sub>)<sub>3</sub>] (<b>3</b>), and (Ph<sub>4</sub>P)<sub>2</sub>[V­(C<sub>3</sub>S<sub>4</sub>O)<sub>3</sub>] (<b>4</b>), with <i>T</i><sub>2</sub>s of 1–4 μs at 80 K in protiated and deuterated environments. Crucially, through chemical tuning of nuclear spin content in the vanadium­(IV) environment we realized a <i>T</i><sub>2</sub> of ∼1 ms for the species (<i>d</i><sub>20</sub>-Ph<sub>4</sub>P)<sub>2</sub>[V­(C<sub>8</sub>S<sub>8</sub>)<sub>3</sub>] (<b>1</b>′) in CS<sub>2</sub>, a value that surpasses the coordination complex record by an order of magnitude. This value even eclipses some prominent solid-state qubits. Electrochemical and continuous wave electron paramagnetic resonance (EPR) data reveal variation in the electronic influence of the ligands on the metal ion across <b>1</b>–<b>4</b>. However, pulsed measurements indicate that the most important influence on decoherence is nuclear spins in the protiated and deuterated solvents utilized herein. Our results illuminate a path forward in synthetic design principles, which should unite CS<sub>2</sub> solubility with nuclear spin free ligand fields to develop a new generation of molecular qubits.