22 research outputs found
Observation of absorptive photon switching by quantum interference
We report an experimental demonstration of photon switching by quantum
interference in a four-level atomic system proposed by Harris and Yamamoto
(Phys. Rev. Lett. 81, 3611 (1998)). Quantum interference inhibits single-photon
absorption but enhances third-order, two-photon type absorption in the
four-level system. We have observed greatly enhanced nonlinear absorption in
the four-level system realized with cold 87Rb atoms and demonstrated fast
switching of the nonlinear absorption with a pulsed pump laser.Comment: 12 pages, 4 figure
Electromagnetically induced transparency and controlled group velocity in a multilevel system
Published versio
Self-assembly of DNA into nanoscale three-dimensional shapes
Molecular self-assembly offers a ‘bottom-up’ route to fabrication with subnanometre precision of complex structures from simple components1. DNA has proven a versatile building block2–5 for programmable construction of such objects, including two-dimensional crystals6, nanotubes7–11, and three-dimensional wireframe nanopolyhedra12–17. Templated self-assembly of DNA18 into custom two-dimensional shapes on the megadalton scale has been demonstrated previously with a multiple-kilobase ‘scaffold strand’ that is folded into a flat array of antiparallel helices by interactions with hundreds of oligonucleotide ‘staple strands’19, 20. Here we extend this method to building custom three-dimensional shapes formed as pleated layers of helices constrained to a honeycomb lattice. We demonstrate the design and assembly of nanostructures approximating six shapes — monolith, square nut, railed bridge, genie bottle, stacked cross, slotted cross — with precisely controlled dimensions ranging from 10 to 100 nm. We also show hierarchical assembly of structures such as homomultimeric linear tracks and of heterotrimeric wireframe icosahedra. Proper assembly requires week-long folding times and calibrated monovalent and divalent cation concentrations. We anticipate that our strategy for self-assembling custom three-dimensional shapes will provide a general route to the manufacture of sophisticated devices bearing features on the nanometer scale