Kazmierczak Nathanael P, Luedecke Kaitlin M, Gallmeier Elisabeth T, Hadt Ryan G
Division of Chemistry and Chemical Engineering, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, California 91125, United States.
J Phys Chem Lett. 2023 Aug 31;14(34):7658-7664. doi: 10.1021/acs.jpclett.3c01964. Epub 2023 Aug 21.
Paramagnetic molecules offer unique advantages for quantum information science owing to their spatial compactness, synthetic tunability, room-temperature quantum coherence, and potential for optical state initialization and readout. However, current optically addressable molecular qubits are hampered by rapid spin-lattice relaxation () even at sub-liquid nitrogen temperatures. Here, we use temperature- and orientation-dependent pulsed electron paramagnetic resonance (EPR) to elucidate the negative sign of the ground state zero-field splitting (ZFS) and assign anisotropy to specific types of motion in an optically addressable = 1 Cr(-tolyl) molecular qubit. The anisotropy displays a distinct sin(2θ) functional form that is not observed in = 1/2 Cu(acac) or other Cu(II)/V(IV) microwave addressable molecular qubits. The Cr(-tolyl) anisotropy is ascribed to couplings between electron spins and rotational motion in low-energy acoustic or pseudoacoustic phonons. Our findings suggest that rotational degrees of freedom should be suppressed to maximize the coherence temperature of optically addressable qubits.
顺磁分子由于其空间紧凑性、合成可调性、室温量子相干性以及光学态初始化和读出的潜力，为量子信息科学提供了独特的优势。然而，即使在低于液氮温度的情况下，当前的光学可寻址分子量子比特仍受到快速自旋 - 晶格弛豫（）的阻碍。在这里，我们使用温度和取向依赖的脉冲电子顺磁共振（EPR）来阐明基态零场分裂（ZFS）的负号，并将 各向异性归因于光学可寻址 = 1 Cr(-甲苯基) 分子量子比特中特定类型的运动。该各向异性呈现出一种独特的sin(2θ)函数形式，这在 = 1/2 Cu(acac) 或其他Cu(II)/V(IV) 微波可寻址分子量子比特中未观察到。Cr(-甲苯基) 各向异性归因于电子自旋与低能声学或准声学声子中的旋转运动之间的耦合。我们的研究结果表明，应抑制旋转自由度，以最大化光学可寻址量子比特的相干温度。
