Boris A. Grishanin

Laser synthesis of chiral molecules in isotropic racemic media

The problem of directional laser synthesis of enantiomers in an isotropic racemic mixture of chiral molecules is analyzed taking into account rotational degrees of freedom of molecules. It is shown that the chirality of the polarization structure of a laser field is the most general necessary condition for the laser distillation of an isotropic non-racemic mixture of chiral molecules with the isotropic distribution over the Eulerian angles. In the approximation of the electric-dipole interaction, the required field configuration can be provided due to noncoplanarity of the polarization vectors of laser-pump components. A relevant experimental scheme is proposed and calculated for the transformation of an isotropic racemic mixture with the help of a three-component pulsed laser field. It is shown that the possibility of the laser control of chirality in an isotropic medium corresponds to nonzero information on coupling between the input and output in the laser field-chiral molecular state information channel.

Stilbene isomerization dynamics on multidimensional potential energy surface. Molecular dynamics simulation

Abstract The dynamics in the photoisomerization of isolated cis-stilbene, especially the dynamics leading to the intermediate twisted configuration is explored by molecular dynamics simulation. Comparison of the dynamics of the trans and cis isomers shows that for cis-stilbene the time required to reach the twisted configuration is an order of magnitude or two less than for trans-stilbene, due only to the specific steric interactions, and not to any difference in the potential functions or parameters. A barrier of between 510 and 640 cm−1 along the torsional coordinate from the cis side is estimated for isolated molecule, accounting for a transition to the intermediate in approximately 300 fs.

Analysis of radiatively stable entanglement in a system of two dipole-interacting three-level atoms

We explore the possibilities of creating radiatively stable entangled states of two three-level dipole-interacting atoms in a \ensuremath{\Lambda} configuration by means of laser biharmonic continuous driving or pulses. We propose three schemes for generation of entangled states which involve only the lower states of the \ensuremath{\Lambda} system, not vulnerable to radiative decay. Two of them employ coherent dynamics to achieve entanglement in the system, whereas the third one uses optical pumping, i.e., an essentially incoherent process.

Coherent-information analysis of quantum channels in simple quantum systems

The coherent information concept is used to analyze a variety of simple quantum systems. Coherent information was calculated for the information decay in a two-level atom in the presence of an external resonant field, for the information exchange between two coupled two-level atoms, and for the information transfer from a two-level atom to another atom and to a photon field. The coherent information is shown to be equal to zero for all full-measurement procedures, but it completely retains its original value for quantum duplication. Transmission of information from one open subsystem to another one in the entire closed system is analyzed to learn quantum information about the forbidden atomic transition via a dipole active transition of the same atom. It is argued that coherent information can be used effectively to quantify the information channels in physical systems where quantum coherence plays an important role.

Generation of Entanglement in a System of Two Dipole-Interacting Atoms by Means of Laser Pulses

Effectiveness of using laser field to produce entanglement between two dipole-interacting identical two-level atoms is considered in detail. The entanglement is achieved by driving the system with a carefully designed laser pulse transferring the systems population to one of the maximally entangled Dicke states in a way analogous to population inversion by a resonant π-pulse in a two-level atom. It is shown that for the optimally chosen pulse frequency, power and duration, the fidelity of generating a maximally entangled state approaches unity as the distance between the atoms goes to zero.

Spectroscopy of Coherent Dark Resonances in Multilevel Atoms for the Example of Samarium Vapor

A universal theory for calculating coherent population trapping resonances in multilevel atoms is suggested. The theory allows arbitrary schemes of multilevel atoms and their excitations to be calculated taking into account the influence of relaxation effects in atoms, applied magnetic field, and the Doppler effect. The experimental data obtained by high-precision diode spectroscopy of coherent dark resonances in samarium vapor are systematically analyzed using the suggested theory. In the absence of a magnetic field, the model of samarium is based on consideration of a degenerate Λ system of the 4f66s2(7F0) ↔ 4f6(7F)6s6p(3P0)9F10↔4f66s2(7F1) active transitions. If the fourth 4f66s2(7F2) level is taken into account, this Λ system becomes open. Numerical simulation of coherent population trapping resonances shows that the open character of the system decreases the contrast of resonance curves in absorption spectra without changing resonance widths. The system under applied external longitudinal and transverse magnetic fields is correctly described by 7-and 12-level models of atomic transitions, respectively.

Photoinduced chirality of hydrogen peroxide molecules

The feasibility of using nonlinear optical techniques to control the chiral states of molecules is examined with the hydrogen peroxide molecule as an example. Raman excitation of optical activity owing to a transition among states with different chiral symmetries is proposed, along with an experimental scheme for detecting the corresponding photoinduced optical rotation in hydrogen peroxide vapor.

Entangling quantum measurements and their properties

We study the mathematical structure of superoperators describing quantum measurements, including the entangling measurement--the generalization of the standard quantum measurement that results in entanglement between the measurable system and apparatus. It is shown that the coherent information can be effectively used for the analysis of such entangling measurements whose possible applications are discussed as well.

Physical implementation of entangling quantum measurements

We clarify the microscopic structure of the entangling quantum measurement superoperators and examine their possible physical realization in a simple three-qubit model, which implements the entangling quantum measurement with an arbitrary degree of entanglement.

Theory of Frequency Modulation Spectroscopy of Coherent Dark Resonances

Theoretical model for the frequency-modulation spectroscopy of dark resonances is discussed in detail on example of a three-level quantum system in A-configuration driven by resonant laser field(s) with and without frequency modulation using two simulation techniques-the density matrix and quantum trajectories analysis.