The isolation of qubits from noise sources, such as surrounding nuclear spins and spin-electric susceptibility , has enabled extensions of quantum coherence times in recent pivotal advances towards the concrete implementation of spin-based quantum computation. In fact, the possibility of achieving enhanced quantum coherence has been substantially doubted for nanostructures due to the characteristic high degree of background charge fluctuations . Still, a sizeable spin-electric coupling will be needed in realistic multiple-qubit systems to address single-spin and spin-spin manipulations . Here, we realize a single-electron spin qubit with an isotopically enriched phase coherence time (20 μs) and fast electrical control speed (up to 30 MHz) mediated by extrinsic spin-electric coupling. Using rapid spin rotations, we reveal that the free-evolution dephasing is caused by charge noise-rather than conventional magnetic noise-as highlighted by a 1/f spectrum extended over seven decades of frequency. The qubit exhibits superior performance with single-qubit gate fidelities exceeding 99.9% on average, offering a promising route to large-scale spin-qubit systems with fault-tolerant controllability.
Both the reversible trans<-->cis photoisomerization and slow thermal back cis-to-trans isomerization of azobenzene-functionalized self-assembled monolayers on gold surfaces have been achieved by rationally designed single-component azobenzene thiol.
We report the successful fabrication of azobenzene-functionalized self-assembled monolayers (SAMs) exhibiting high and reversible photoswitching between trans and cis states on a flat gold surface. Azobenzene thiols (MeSH and EtSH) containing meta and/or ortho substituents were chosen based on the occupied area per molecule as well as intermolecular interactions between the azobenzene aromatic rings (formation of H-aggregates). Theoretical predictions of the geometrical structures were performed to clarify the correlation between the molecular structure and photoisomerization characteristics in monolayer systems. The striking difference in absorption spectra of a trans-EtSH SAM and a cis-EtSH SAM by alternating UV and visible light irradiation was in good agreement with that in their contact angles for water, strongly indicating that the structural changes were controlled by light wavelength. By contrast, despite there being sufficient free space for each MeSH molecule, the strong tendency of the planar azobenzene units to generate H-aggregates even during cis-MeSH SAM formation lessened the trans-to-cis photoisomerization yield in a monolayer.
A delicate balance between space, intermolecular interactions, and phase separation plays an important role in forming repeatedly photoswitchable monolayers.
The photoisomerization characteristics of sterically hindered azobenzenes in self-assembled monolayers (SAMs) on flat gold surfaces have been investigated by ultraviolet–visible (UV–vis) absorption spectroscopy and contact angle measurements. Upon UV light irradiation, 2Et-2S substituted with two ethyl groups at the ortho positions and Me-2S with a methyl group at the meta position showed significant changes in π–π* absorption bands, together with reductions in contact angles for water, as a consequence of trans-to-cis photoisomerization. The reversible trans ↔ cis photoisomerization of azobenzenes in SAMs was clearly observed upon alternating UV and visible light irradiation. Furthermore, 2Et-2S underwent very slow thermal cis-to-trans isomerization over 24 h at ambient temperature, which is likely to be due to the steric hindrance of diethyl groups near the azo linkage.
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