Biomedical subjects

Petr Král

Publications and source records attributed to Petr Král.

4 recordsLinked to original sources

PubMed2003

Two-step enantio-selective optical switch.

We present an optical "enantio-selective switch" that, in two steps, turns a ("racemic") mixture of left-handed and right-handed chiral molecules into the enantiomerically pure state of interest. The optical switch is composed of an "enantio-discriminator" and an "enantio-converter" acting in tandem. The method is robust, insensitive to decay processes, and does not require molecular preorientation. We demonstrate the method on the purification of a racemate of (transiently chiral) D2S2 molecules, performed on the nanosecond time scale.

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PubMed2002

Highly extended image states around nanotubes.

We predict that freely suspended, linear molecular conductors or dielectrics, such as carbon nanotubes, can support electronic states that are localized far from the surface. These "tubular image states" are formed in extended potential wells resulting from the tug of war between the external electron's attraction to its image charge in the nanotube, and its repulsion from the tube due to its transverse angular momentum. The displacement of these states (>10 nm) away from the surface prevents their wave functions from collapsing, resulting in long lifetimes at low temperatures. We predict that tubular image states with binding energies of 1-10 meV can be formed via radiative recombination.

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PubMed2002

Analytic solution for the nondegenerate quantum control problem.

We present an analytic solution for the nondegenerate quantum control problem, i.e., the transfer of a deliberate amount of population, 0%-100%, between arbitrary initial Psi(t)> and final Psi'(t)> states, which can be expanded in terms of nondegenerate energy eigenstates k>. The solution constitutes a robust two-photon multicomponent adiabatic passage, via an intermediate eigenstate 0>, which relies on three types of "null states."

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PubMed2002

Electric polarization of heteropolar nanotubes as a geometric phase.

The threefold symmetry of planar boron nitride (BN), the III-V analog to graphene, prohibits an electric polarization in its ground state, but this symmetry is broken when the sheet is wrapped to form a BN nanotube. We show that this leads to an electric polarization along the nanotube axis which is controlled by the quantum mechanical boundary conditions on its electronic states around the tube circumference. Thus the macroscopic dipole moment has an intrinsically nonlocal quantum mechanical origin from the wrapped dimension. We formulate this novel phenomenon using the Berry's phase approach and discuss its experimental consequences.

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