Mao Haochuan, Pažėra Gediminas J, Young Ryan M, Krzyaniak Matthew D, Wasielewski Michael R
Department of Chemistry, Center for Molecular Quantum Transduction, and Institute for Sustainability and Energy at Northwestern, Northwestern University, Evanston, Illinois 60208-3113, United States.
Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3QZ, U.K.
J Am Chem Soc. 2023 Mar 22;145(11):6585-6593. doi: 10.1021/jacs.3c01243. Epub 2023 Mar 13.
Sub-nanosecond photodriven electron transfer from a molecular donor to an acceptor can be used to generate a radical pair (RP) having two entangled electron spins in a well-defined pure initial singlet quantum state to serve as a spin-qubit pair (SQP). Achieving good spin-qubit addressability is challenging because many organic radical ions have large hyperfine couplings (HFCs) in addition to significant -anisotropy, which results in significant spectral overlap. Moreover, using radicals with -factors that deviate significantly from that of the free electron results in difficulty generating microwave pulses with sufficiently large bandwidths to manipulate the two spins either simultaneously or selectively as is necessary to implement the controlled-NOT (CNOT) quantum gate essential for quantum algorithms. Here, we address these issues by using a covalently linked donor-acceptor(1)-acceptor(2) (D-A-A) molecule with significantly reduced HFCs that uses fully deuterated -xanthenoxanthene (PXX) as D, naphthalenemonoimide (NMI) as A, and a C derivative as A. Selective photoexcitation of PXX within PXX--NMI-C results in sub-nanosecond, two-step electron transfer to generate the long-lived PXX--NMI-C SQP. Alignment of PXX--NMI-C in the nematic liquid crystal 4-cyano-4'-(-pentyl)biphenyl (5CB) at cryogenic temperatures results in well-resolved, narrow resonances for each electron spin. We demonstrate both single-qubit gate and two-qubit CNOT gate operations using both selective and nonselective Gaussian-shaped microwave pulses and broadband spectral detection of the spin states following the gate operations.
亚纳秒级的光驱动电子从分子供体转移到受体可用于产生一个自由基对（RP），该自由基对在定义明确的纯初始单重态量子态中具有两个纠缠的电子自旋，可作为自旋量子比特对（SQP）。实现良好的自旋量子比特可寻址性具有挑战性，因为许多有机自由基离子除了具有显著的各向异性外，还具有大的超精细耦合（HFC），这导致显著的光谱重叠。此外，使用g因子与自由电子的g因子有显著偏差的自由基会导致难以产生具有足够大带宽的微波脉冲，以便像实施量子算法所必需的受控非门（CNOT）量子门那样同时或选择性地操纵两个自旋。在这里，我们通过使用一种共价连接的供体 - 受体(1)-受体(2)（D - A - A）分子来解决这些问题，该分子具有显著降低的HFC，它使用全氘代的呫吨并呫吨（PXX）作为供体D，萘单酰亚胺（NMI）作为受体A，以及一种C衍生物作为受体A。在PXX - NMI - C内对PXX进行选择性光激发会导致亚纳秒级的两步电子转移，从而产生长寿命的PXX - NMI - C SQP。在低温下将PXX - NMI - C排列在向列型液晶4 - 氰基 - 4'-（戊基）联苯（5CB）中会导致每个电子自旋具有分辨率良好的窄共振。我们使用选择性和非选择性高斯形微波脉冲以及门操作后自旋态的宽带光谱检测，展示了单量子比特门和双量子比特CNOT门操作。
