Heterodimetallic [LnLn′] Lanthanide Complexes: Toward a Chemical Design of Two-Qubit Molecular Spin Quantum Gates

A major challenge for realizing quantum computation is finding suitable systems to embody quantum bits (qubits) and quantum gates (qugates) in a robust and scalable architecture. An emerging bottom-up approach uses the electronic spins of lanthanides. Universal qugates may then be engineered by arranging in a molecule two interacting and different lanthanide ions. Preparing heterometallic lanthanide species is, however, extremely challenging. We have discovered a method to obtain [LnLn′] complexes with the appropriate requirements. Compound [CeEr] is deemed to represent an ideal situation. Both ions have a doubly degenerate magnetic ground state and can be addressed individually. Their isotopes have mainly zero nuclear spin, which enhances the electronic spin coherence. The analogues [Ce2], [Er2], [CeY], and [LaEr] have also been prepared to assist in showing that [CeEr] meets the qugate requirements, as revealed through magnetic susceptibility, specific heat, and EPR. Molecules could now be used for quantum information processing.实现量子计算的核心挑战之一，在于如何在稳健且可扩展的架构中，找到能够承载量子比特（qubits）与量子门（qugates）的合适物理系统。当下一种新兴的自下而上研究策略，以镧系元素的电子自旋作为载体。通过在单个分子中排布两种相互作用且种类不同的镧系离子，即可构建出通用量子门。然而，制备异金属镧系配合物极具挑战性。我们已开发出一种可合成符合应用要求的[LnLn′]型配合物的方法，其中[CeEr]配合物被认为是理想的模型体系。该体系中的两种离子均具有二重简并的磁基态，且可被单独寻址；它们的同位素核自旋大多为零，这一特性能够有效提升电子自旋相干性。为验证[CeEr]满足量子门的应用要求，我们还同步制备了[Ce₂]、[Er₂]、[CeY]与[LaEr]作为对照体系，并通过磁化率、比热容以及电子顺磁共振（Electron Paramagnetic Resonance, EPR）表征手段证实了这一点。本研究证明，分子体系可应用于量子信息处理领域。