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Nanotubes Findings

Nanotubes Findings

Studied are the interactions of the excitonic states with surface electromagnetic modes of small-diameter (< ~1 nm) semiconducting single-walled carbon nanotubes. It has been shown that these interactions can result in strong exciton-surface-plasmon coupling. The exciton absorption lineshapes exhibit the line (Rabi) splitting ~0.1 eV as the exciton energy is tuned to the nearest interband surface plasmon resonance of the nanotube. Quantum confined Stark effect is shown to be capable of tuning the exciton excitation energy to the nearest plasmon resonance. This effect is very challenging for the experimental realization. It opens up a path to new tunable optoelectronic device applications of semiconducting carbon nanotubes in areas such as nanoplasmonics, nanophotonics and cavity quantum electrodynamics. [Figure 1; PHYSICAL REVIEW B 80, 085407 (2009); OPTICS COMMUNICATIONS 282, 661 (2009)].

**Fig. 1**

Calculated exciton-plasmon parameters for the (11,0) CN. (a)Dimensionless axial surface conductivity [interband plasmon resonances are the peaks of Re(1/szz)]. (b)Dispersion curves exhibit clear anticrossing behavior for the 1st bright exciton coupled to the nearest interband plasmon resonance. (c)Perpendicular electrostatic field brings together the 1st bright exciton excitation energy and plasmon energy, and narrows the band gap [all measured from the top of the 1st unperturbed hole subband]. (d)Exciton absorption/emis-sion lineshapes show Rabi splitting as the exciton total energy is tuned to the nearest plasmon resonance (dashed line). Dimensionless energy is defined as [Energy]/2?0 where ?0=2.7 eV is the C-C nearest neighbor overlap integral.

van de Waals potential energy between two parallel radially deformed single-walled carbon nanotubes is calculated. The most preferred mutual nanotube orientations are identified in terms of potential well depths, equilibrium distances, and geometrical parameters. It is found that the interaction evolves in such a way as to keep the distance between the interacting surfaces comparable to the graphene-graphene distance in graphite. The universal graphitic potential concept is extended to radially deformed carbon nanotubes. These results may be used as a guide for experiments investigating interactions between deformed carbon nanotubes, and their sensory properties. [Figure 2; PHYSICAL REVIEW B 77, 115443 (2008)].

**Fig. 2.**

Calculated van der Waals potentials for two parallel cylindrical (a) and elliptically deformed (b) carbon nanotubes.

A double wall carbon nanotube oscillator near an infinite surface with the nanotube axis perpendicular to the surface is investigated. The oscillatory motion is governed by internanotube van der Waals forces and friction losses due to the proximity of the surface under investigation. The oscillatory motion has been studied as a function of the nanotube-surface distance, nanotube length, and the initial extrusion of the moving nanotube. A practical nanotube based surface profiling device is proposed, and is shown to have better in-plane resolution than typical AFM devices currently in use. [Figure 3; NANOTECHNOLOGY 19, 435702 (2008)].

Modeling of the atomic structure and spin properties of the Eu@C82 and Eu@C60 endohedral structures have been performed by means of the quantum-chemical DFT method. We consider the case where the Eu atom is located inside of the fullerene. Relaxations of the endohedral structures relative to their initial position are studied. Calculated atomic, electronic and spin distributions (hyperfine contact coupling constants and spin densities) for the considered structures are compared with those for the Sc@C82 complex. The complexes studied are shown to satisfy with the basic requirement to be the candidates for spin qubits, that is the strong localization of the electron spin density on the Eu nucleus. [XII International Conference on Quantum Optics and Quantum Information, Vilnius, Lithuania, September 20–23, 2008, book of abstracts, talk Su21E(P)6, p.43]

**Fig. 04: Left panel:** Relaxed Eu@C82 complex after annealing.

Modeling of the atomic structure and spin properties of the Eu@C82 and Eu@C60 endohedral structures have been performed by means of the quantum-chemical DFT method. We consider the case where the Eu atom is located inside of the fullerene. Relaxations of the endohedral structures relative to their initial position are studied. Calculated atomic, electronic and spin distributions (hyperfine contact coupling constants and spin densities) for the considered structures are compared with those for the Sc@C82 complex. The complexes studied are shown to satisfy with the basic requirement to be the candidates for spin qubits, that is the strong localization of the electron spin density on the Eu nucleus.[XII International Conference on Quantum Optics and Quantum Information, Vilnius, Lithuania, September 20–23, 2008, book of abstracts, talk Su21E(P)6, p.43]

Investigated is the entanglement effect between two quasi-one-dimensional atomic polariton states formed by the two two-level atoms (or ions) located close to or encapsulated inside carbon nanotubes and strongly coupled to the nanotube virtual photonic modes (Figure). Small-diameter metallic nanotubes are shown to result in sizable amounts of the two-qubit atomic entanglement (each two-level atom represents a qubit – a quantum bit, the basic unit of quantum information), which coherently persists with no damping for very long times. Materials that may host quantum coherent states with long coherence lifetimes is a critical research problem. New calculations of the NCCU group open paths to novel applications of atomically doped carbon nanotubes in solid-state quantum information science. [I.V.Bondarev and B.Vlahovic, Physical Review B 75, 033402 (2007); ibid. 74, 073401 (2006)]

**Fig. 5:Left panel:** Schematic of the two atoms, atom A and atom B, coupled to the common virtial surface photonic mode of the carbon nanotube.