A fault-tolerant quantum processor may be configured using stationary qubits interacting only with their nearest neighbours, but at the cost of significant overheads in physical qubits per logical qubit. Such overheads could be reduced by coherently transporting qubits across the chip, allowing connectivity beyond immediate neighbours. Here we demonstrate high-fidelity coherent transport of an electron spin qubit between quantum dots in isotopically-enriched silicon. We observe qubit precession in the inter-site tunnelling regime and assess the impact of qubit transport using Ramsey interferometry and quantum state tomography techniques. We report a polarization transfer fidelity of 99.97% and an average coherent transfer fidelity of 99.4%. Our results provide key elements for high-fidelity, on-chip quantum information distribution, as long envisaged, reinforcing the scaling prospects of silicon-based spin qubits.
A complete set of new photolabile nucleoside phosphoramidites were synthesized, then site-specifically incorporated into sense or antisense strands of siRNA for phosphate caging. Single caging modification was made along siRNA strands and their photomodulation of gene silencing were examined by using the firefly luciferase reporter gene. Several key phosphate positions were then identified. Furthermore, multiple caging modifications at these key positions led to significantly enhanced photomodulation of gene silencing activity, suggesting a synergistic effect. The caging group on both the terminally phosphate-caged siRNA and the single-stranded caged RNA has comparatively high stability, whereas hydrolysis of the caged group from the internally caged siRNA was observed, irrespective of the presence of Mg(2+). Molecular dynamic simulations demonstrated that enhanced hydrolysis of the caging group on internally phosphate-caged siRNAs was due to easy fragmentation of the caging group upon formation of the pentavalent intermediate of the phosphotriester with attack by water. The caging group in the terminally phosphate-caged siRNA or single-stranded caged RNA prefers to form π-π stacks with nearby nucleobases. In addition to providing explanations for previous observations, this study sheds further light on the design of caged oligonucleotides and indicates the direction of future development of nucleic acid drugs with phosphate modifications.
There are minor errors in the evolution expression in the left column, the second page. The corresponding evolution should be as follows:where G 1 Ј= ͱ 2 1 2 −9 2 / 16 and others are of the same definitions as in the paper. If we choose the evolution time of the system to be t 1 = ͓ arctan ͑ 4G 1 ͒ +8 ͔ / G 1 , we have sin͑G 1 Јt 1 ͒ Ͻ 0.065Ӎ 0 and cos͑G 1 Јt 1 ͒ Ͼ 0.998 for a small cavity decay Ͻ 0.06 1 . Due to the above modification, there are some changes for the prepared cluster state. The fidelity for the prepared cluster state is decreased, and the maximal qubit number of the cluster state is only 12 for a fidelity F Ͼ 0.95. As our scheme works validly only in the regime of / 1, however, our treatment in the paper still remains a good approximation, while Fig. 2 in the paper should be modified as shown below. This modification has no effect on the second part of the paper, i.e., for preparation of W states.*Electronic address: xili-zhang@hotmail.com † Electronic address: mangfeng1968@yahoo. com FIG. 2. The fidelity and the success probability versus the cavity decay in the generation of a cluster state, where the solid, dashed, and dashed-dotted lines represent the consideration with the time delay a = 0, 0.01 , 0.05 for adjusting level spacing, respectively, with the desired time in the perfect case. The curves from the top to bottom correspond to N =2,3, and 4. For simplicity, we have assumed the same coupling strength for each SQUID qubits to the radiation fields, i.e., i = ͑i =1,2,3, . . . .͒ PHYSICAL REVIEW A 74, 059901͑E͒ ͑2006͒
Caged siRNAs with a circular structure were successfully used for photoregulation of target genes in both cells and mice.
A series of Vitamin E (vitE)-labeled PEIs (PEI-vitE) were synthesized and showed excellent complexation ability with plasmid DNA (pDNA). The cellular uptake of PEI-vitE/pDNA complexes was greatly enhanced with the increase of vitE labeling, which is much better than that of control PEI25 in three different cell lines. PEI-vitE showed the best performance in gfp pDNA delivery and following GFP expression in HEK-293A cells. In addition, in vivo gene delivery in living mice also confirmed that PEI-vitE showed low toxicity and efficiently delivered gfp pDNA to the cells of liver and lung tissues for gene expression.
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