Yuichi Fujimura

Control of quantum dynamics by a locally optimized laser field. Application to ring puckering isomerization

We presented a theoretical method for controlling quantum dynamics by locally optimized nonstationary laser fields, within the semiclassical theory of the molecule–radiation field interaction. The external laser field is optimized based on the control theory of a linear time‐invariant (LTI) system, so that both the summation of the population of the nontarget states and the total energies of the laser fields are minimized. The optimization procedure involves operation of the so‐called feedback gain matrix to the time‐dependent state vector. This procedure is carried out at every successive short stage, in which the time‐dependent Schrodinger equation can be approximated to the equation of motion of the LTI system. As an example, the control theory was applied to laser‐induced ring‐puckering isomerization, the dynamics of which can be described as the wave packet in the one‐dimensional double minimum potential under locally optimized laser fields. The result indicated that nearly 100% of the population can...

TWO-FREQUENCY IR LASER ORIENTATION OF POLAR MOLECULES. NUMERICAL SIMULATIONS FOR HCN

Abstract Using ab initio nuclear-coordinate-dependent dipole moments and polarizabilities, we study the orientation dynamics of HCN, by numerically solving the time-dependent Schrodinger equation, in the presence of a superposition of intense, linearly-polarized infrared laser pulses of frequency ω and 2ω. We show that polarizability acts in concert with permanent dipole moments to orient polar molecules, as opposed to alignment which occurs alone with a single laser frequency or one moment only (permanent or induced). Optimal orientation occurs for the field configuration E (t)= E 0 (t) cos ωt+0.5 cos 2ωt , where 2ω is resonant with a 0 → 1 vibrational transition and E 0 (t) is a picosecond pulse.

ADIABATIC AND DIABATIC RESPONSES OF H2+ TO AN INTENSE FEMTOSECOND LASER PULSE : DYNAMICS OF THE ELECTRONIC AND NUCLEAR WAVE PACKET

We investigate the quantal dynamics of the electronic and nuclear wave packet of H2+ in strong femtosecond pulses (⩾1014 W/cm2). A highly accurate method which employs a generalized cylindrical coordinate system is developed to solve the time-dependent Schrodinger equation for a realistic three-dimensional (3D) model Hamiltonian of H2+. The nuclear motion is restricted to the polarization direction z of the laser electric field E(t). Two electronic coordinates z and ρ and the internuclear distance R are treated quantum mechanically without using the Born-Oppenheimer approximation. As the 3D packet pumped onto 1σu moves toward larger internuclear distances, the response to an intense laser field switches from the adiabatic one to the diabatic one; i.e., electron density transfers from a well associated with a nucleus to the other well every half optical cycle, following which interwell electron transfer is suppressed. As a result, the electron density is asymmetrically distributed between the two wells. Co...

Selective preparation of enantiomers by laser pulses: quantum model simulation for H2POSH

Abstract This Letter presents the first quantum model simulation of the selective preparation of enantiomers by means of optimal, elliptically polarized, infrared picosecond laser pulses. The laser-driven molecular dynamics is demonstrated by the time evolution of the representative wavepacket, from the initial state which corresponds to a 50:50% racemate of two equivalent enantiomers with opposite chiralities towards the nearly 100:0% preparation of a single enantiomer. The wavepacket dynamics is based on the quantum ab initio potential energy surface and dipole functions for the torsional vibration of the hydrogen atom around the P–S molecular axis of the model system H 2 POSH.

Geometric phase effects in the coherent control of the branching ratio of photodissociation products of phenol

Optimal control simulation is used to examine the control mechanisms in the photodissociation of phenol within a two-dimensional, three-electronic-state model with two conical intersections. This model has two channels for H-atom elimination, which correspond to the (2)pi and (2)sigma states of the phenoxyl radical. The optimal pulse that enhances (2)sigma dissociation initially generates a wave packet on the S(1) potential-energy surface of phenol. This wave packet is bifurcated at the S(2)-S(1) conical intersection into two components with opposite phases because of the geometric phase effect. The destructive interference caused by the geometric phase effect reduces the population around the S(1)-S(0) conical intersection, which in turn suppresses nonadiabatic transitions and thus enhances dissociation to the (2)sigma limit. The optimal pulse that enhances S(0) dissociation, on the other hand, creates a wave packet on the S(2) potential-energy surface of phenol via an intensity borrowing mechanism, thus avoiding geometric phase effects at the S(2)-S(1) conical intersection. This wave packet hits the S(1)-S(0) conical intersection directly, resulting in preferred dissociation to the (2)pi limit. The optimal pulse that initially prepares the wave packet on the S(1) potential-energy surface (PES) has a higher carrier frequency than the pulse that prepares the wave packet on the S(2) PES. This counterintuitive effect is explained by the energy-level structure and the S(2)-S(1) vibronic coupling mechanism.

Locally designed pulse shaping for selective preparation of enantiomers from their racemate

We present a method for the design of laser fields to control a selective preparation of enantiomers from their racemate. An expression for two components of the laser pulses [EX(t) and EY(t)] propagating along the Z axis is derived using a locally optimized control theory in the density operator formalism. This expression was applied to a selective preparation of (R-, L-) enantiomers from preoriented phosphinotioic acid (H2POSH) at low temperatures. The target operator was set for the populations to be localized in one side of the double-well potential. First, a simple one-dimensional model was treated. Then, a two-dimensional model in which a free rotation around the preoriented torsional axis is included was briefly considered. In the one-dimensional model, almost complete preparation of the enantiomers was obtained. The optimal electric field consists of a sequence of two linearly polarized pulses with the same phases but with different magnitudes. This means that the resultant electric field is linea...

Quantum Control of nuclear wave packets by locally designed optimal pulses

A new approach to locally design a control pulse is proposed. This locally optimized control pulse is explicitly derived, starting with optimal control formalism, and satisfies the necessary condition for a solution to the optimal control problem. Our method requires a known function, g(t), a priori, which gives one of the possible paths within the functional space of the objective functional. A special choice of g(t)≡0 reduces the expression of the control pulse to that derived by Kosloff et al. For numerical application, we restrict ourselves to this special case; however, by combining an appropriate choice of the target operator together with the backward time-propagation technique, we apply the local control method to population inversion and to wave packet shaping. As an illustrative example, we adopt a two-electronic-surface model with displaced harmonic potentials and that with displaced Morse potentials. It is shown that our scheme successfully controls the wave packet dynamics and that it can be ...

Exact two-electron wave packet dynamics of H2 in an intense laser field: Formation of localized ionic states H+ H–

We have developed an efficient grid method that can accurately deal with the electronic wave packet dynamics of two-electron systems in three-dimensional (3D) space. By using the dual transformation technique, we remove the numerical difficulties arising from the singularity of the attractive Coulomb potential. Electron–electron repulsion is incorporated into the wave packet propagation scheme without introducing any approximations. The exact electronic dynamics of H2 is simulated for the first time. At small internuclear distances (e.g., R=4 a.u.), an ionic component characterized by the structure H+H− is created in an intense laser field E(t) (intensity>1013 W/cm2 and λ≈720 nm) because an electron is transferred from the nucleus around which the dipole interaction energy for the electron becomes higher with increasing |E(t)|. The localized ionic structure is identified with the H− anion at the nucleus around which the dipole interaction energy becomes lower. Tunneling ionization proceeds via the formati...

Quantum optimal control of multiple targets: Development of a monotonically convergent algorithm and application to intramolecular vibrational energy redistribution control

An optimal control procedure is presented to design a field that transfers a molecule into an objective state that is specified by the expectation values of multiple target operators. This procedure explicitly includes constraints on the time behavior of specified operators during the control period. To calculate the optimal control field, we develop a new monotonically and quadratically convergent algorithm by introducing a quadruple space that consists of a direct product of the double (Liouville) space. In the absence of the time-dependent constraints, the algorithm represented in the quadruple-space notation reduces to that of the double-space notation. This simplified formulation is applied to a two dimensional system which models intramolecular vibrational energy redistribution (IVR) processes in polyatomic molecules. An optimal pulse is calculated that exploits IVR to transfer a specific amount of population to an optically inactive state, while the other portion of the population remains in the initial state at a control time. Using trajectory plots in quantum-number space, we numerically analyze how the control pathway changes depending on the amount of the excited population.

Optimal control of quantum non-Markovian dissipation: reduced Liouville-space theory.

An optimal control theory for open quantum systems is constructed containing non-Markovian dissipation manipulated by an external control field. The control theory is developed based on a novel quantum dissipation formulation that treats both the initial canonical ensemble and the subsequent reduced control dynamics. An associated scheme of backward propagation is presented, allowing the efficient evaluation of general optimal control problems. As an illustration, the control theory is applied to the vibration of the hydrogen fluoride molecule embedded in a non-Markovian dissipative medium. The importance of control-dissipation correlation is evident in the results.