Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States.
Chemical Sciences and Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
J Am Chem Soc. 2016 Nov 9;138(44):14678-14685. doi: 10.1021/jacs.6b08467. Epub 2016 Oct 31.
Quantum information processing (QIP) offers the potential to create new frontiers in fields ranging from quantum biology to cryptography. Two key figures of merit for electronic spin qubits, the smallest units of QIP, are the coherence time (T), the lifetime of the qubit, and the spin-lattice relaxation time (T), the thermally defined upper limit of T. To achieve QIP, processable qubits with long coherence times are required. Recent studies on (PhP-d)[V(CS)], a vanadium-based qubit, demonstrate that millisecond T times are achievable in transition metal complexes with nuclear spin-free environments. Applying these principles to vanadyl complexes offers a route to combine the previously established surface compatibility of the flatter vanadyl structures with a long T. Toward those ends, we investigated a series of four qubits, (PhP)[VO(CS)] (1), (PhP)[VO(β-CS)] (2), (PhP)[VO(α-CS)] (3), and (PhP)[VO(CSO)] (4), by pulsed electron paramagnetic resonance (EPR) spectroscopy and compared the performance of these species with our recently reported set of vanadium tris(dithiolene) complexes. Crucially we demonstrate that solutions of 1-4 in SO, a uniquely polar nuclear spin-free solvent, reveal T values of up to 152(6) μs, comparable to the best molecular qubit candidates. Upon transitioning to vanadyl species from the tris(dithiolene) analogues, we observe a remarkable order of magnitude increase in T, attributed to stronger solute-solvent interactions with the polar vanadium-oxo moiety. Simultaneously, we detect a small decrease in T for the vanadyl analogues relative to the tris(dithiolene) complexes. We attribute this decrease to the absence of one nuclear spin-free ligand, which served to shield the vanadium centers against solvent nuclear spins. Our results highlight new design principles for long T and T times by demonstrating the efficacy of ligand-based tuning of solute-solvent interactions.
量子信息处理（QIP）有望在从量子生物学到密码学等领域开辟新的前沿。电子自旋量子比特的两个关键衡量标准是相干时间（T），即量子比特的寿命，以及自旋晶格弛豫时间（T），即 T 的热定义上限。为了实现 QIP，需要具有长相干时间的可处理量子比特。最近对基于钒的量子比特（PhP-d）[V（CS）]的研究表明，在具有无核自旋环境的过渡金属配合物中可以实现毫秒级 T 时间。将这些原理应用于钒氧基配合物提供了一种结合先前建立的平坦钒氧基结构的表面兼容性和长 T 的途径。为此，我们通过脉冲电子顺磁共振（EPR）光谱研究了一系列四个量子比特，（PhP）[VO（CS）]（1），（PhP）[VO（β-CS）]（2），（PhP）[VO（α-CS）]（3）和（PhP）[VO（CSO）]（4），并将这些物种的性能与我们最近报道的一系列钒三（二硫烯）配合物进行了比较。至关重要的是，我们证明了在 SO 中 1-4 的溶液，一种独特的无核自旋极性溶剂，显示出高达 152(6)μs 的 T 值，与最佳的分子量子比特候选物相当。从三（二硫烯）类似物过渡到钒氧基物种时，我们观察到 T 值显著增加了一个数量级，这归因于极性钒-氧键的更强的溶质-溶剂相互作用。同时，我们检测到钒氧基类似物的 T 值相对于三（二硫烯）配合物略有下降。我们将这种下降归因于缺少一个无核自旋的配体，该配体可保护钒中心免受溶剂核自旋的影响。我们的结果通过证明配体基对溶质-溶剂相互作用的调谐的有效性，突出了长 T 和 T 时间的新设计原则。
